Tài liệu Mold Cost, Mold Price and Delivery pptx

159 5 Mold Cost, Mold Price and Delivery 5.1 Mold Cost and Records Some of the following may be obvious to the reader, but it is surprising how many mold makers and their staff do not keep proper records. The decision makers must be aware of the methods used by mold makers to arrive at a mold cost and mold price. They will then better understand what is involved when negotiating the purchase of any mold or special equipment used to increase production and to improve productivity. The mold cost is the total of the actual costs incurred to make a mold, which include general plant overhead, but does not include any addition for risk and profit as will be discussed later. It is the sum of all moneys spent for raw materials, hardware, and services, plus the total of the time (hours) used by designers, machinists, assemblers, and other technicians involved in building a mold and any additional equipment required for this mold, multiplied by the hourly wage (or salary) rates, which will include all employee benefits provided. Added to this is the plant overhead rate. Hourly rates and/or overhead rates used in these calculations can be different for different employees or groups of employees and for different equipment used; or, there can be a single, plant-wide rate. Overhead costs can also be included in the hourly rates, so that the actual rate used to arrive at the mold cost consists of, for example, $18.00 (actual hourly pay to the employee), plus $12.00 (employee’s benefits), plus $25.00 (overhead rate) for a total rate of $55.00 per hour to be used when calculating the mold cost. In order to arrive at an accurate mold cost it is therefore important (1) To have a complete and clearly understood Bill of Materials (BoM), and component drawings, (2) To record all the funds spent for purchased items and services, (3) To have a method of recording conscientiously the actual times spent on this job by each employee, e.g., by filling out time cards, and (4) To have clearly defined hourly rates The old-fashioned method was to have the BoM shown on the assembly drawing. This used to be satisfactory with simple dies or molds, but is not practical for today’s molds, which often consist of many components. It is also not convenient for a buyer or accountant to work with an often unwieldy, large drawing. Major costs to make a mold:  Raw materials  Direct labor (hours)  Machining costs (hours)  Purchased components  Equipment depreciation  Testing costs (hours)  Overhead  Plant costs Keep proper records of any job! 1281han05.pmd 28.11.2005, 11:08159 160 5 Mold Cost, Mold Price and Delivery The mold maker must make sure that only materials and times necessary for the mold as designed (originally planned) are included in the actual mold cost. Neither time, nor materials required to make changes to correct any design or manufacturing errors while building the mold, nor any costs which were found necessary to be added after the mold was tested before shipping should be included in the actual mold cost, if these costs were not anticipated when estimating. These additional costs will unfortunately eat into the profit margin, because they cannot be billed to the customer. These changes and corrections, as well as their reasons, must be properly recorded, so that they will be remembered when using this record for a repeat order of the same mold or for future estimates of similar molds. All mold makers should keep a special “job file” for every mold built, in numerical order of jobs, by subject, and possibly also by customer, and keep it in one central location rather than in the memory or in the files of individual employees. Changes in personnel are unavoidable and it is quite common that much important data is lost when an employee leaves. These records must include the original cost estimate, a copy of the purchase order or sales contract, the confirmation of order, the BoM, the actual cost data, and the test report of the mold (or the system). Any significant information gathered about the performance of the mold at the molder after delivery and any complaints or changes that were necessary to make and any other information that could be valuable for future, similar molds can then be added to the file at later dates, as they occur. 5.1.1 Spare Parts for the Mold This is an often-overlooked area. Today, especially with high production molds, there are some delicate, easily damaged mold parts such as mold pins. Other parts, such as gate inserts, stripper rings, ejector pins and sleeves, and other moving parts are subject to wear. In addition, there are electrical heaters and thermocouples that may have a limited service life. It is also a good idea to have the proper size O-rings on hand when dismantling and re-assembling a mold, to make sure there won’t be any water leaks. Mold spare parts will be much less expensive to make while the mold is being built in the first place than to have them built when needed. It is good practice to have such spare parts on hand when buying a mold and this should always be included in a mold order. While they add to the mold cost, the will save much time when the mold needs repairs and ensure minimum downtime. It is up to the mold maker to suggest the spare parts to be recommended to the buyer at the time of the mold order. Always create job files for every project (molds, etc.) For multi-cavity molds, a rule of thumb is to order 5% spare parts and round up It is always a good idea to order spares at the time of the mold. The cost to produce another piece will be much lower 1281han05.pmd 28.11.2005, 11:08160 161 5.1 Mold Cost and Records 5.1.2 The Basic Elements of the Mold Cost The total mold cost consists of a number of costs directly attributable and necessary for the making of a mold, as detailed in the following sections. 5.1.2.1 Designing the Mold, Including Checking of Drawings Design of a mold can sometimes require considerable time. The time required is not necessarily related to the size, but always to the complexity of the product and to the performance features expected of the mold. Design time can range from 10 to 15% of the total hours estimated for the mold, but could be as high as 20% or even more. But this time is not wasted: always remember it is easier to change the designs at an early stage than to change the steel once cutting has started. CAD (Computer Assisted Design) has revolutionized design practices, but is really most useful when applied in conjunction with standardization of designs of mold details. The more hardware, mold features, or entire molds are standardized and in the memory of the computer, the less design time will be required. But this does not imply that there is not ample room for the ingenuity on the part of the designers and it must be understood that there is no progress without change. It may be necessary to deviate from established standards and sometimes to change them partly or altogether, if a better design can be found. But the overall target must never be forgotten: While a proposed design change could improve one area, e.g., the mold performance, it could negatively affect another area, such as mold life or the manufacturing process, so that the final cost of the product could increase. Another area that must not be overlooked is delivery time. Mold deliveries are always urgent and critical. Molds are usually required “as soon as possible” and for this reason alone it is often better to stick with existing, reliable standards. They assist not only during the design phase but also in machining operations that may also have standard procedures, and even specially equipped machines and fixtures to facilitate the making of mold parts. Checking of drawings is often overlooked or ignored, but it is very important; at least 10% of the design time should be dedicated for checking. Checking is much simplified with CAD, because the computer performs most calcu- lations, but it is important to make sure that the data input was correct. Checking for dimensions is only part of the process. The checker must also make sure that the final mold design covers all design features required by the product design, all fits and clearances for the mold, and much more. Any error can be very costly. Having a responsible checker, preferably another experienced designer (never the original designer!) looking at the drawings before they reach the manufacturing phase will be much less expensive than having to fix errors later. Figure 5.2 shows the various design and manufacturing steps in relation to the time needed for completion (usually weeks). The description on the graph is self-explanatory. Figure 5.1 Mold designer working at a CAD station From experience, it is practically impossible to check one’s own designs and drawings 1281han05.pmd 28.11.2005, 11:08161 162 5 Mold Cost, Mold Price and Delivery 5.1.2.2 Materials The cost of material is usually about 10–15% of the mold cost, and may be as high as 20% or even more, in large but otherwise simple molds. Raw Materials The deciding factor when selecting steels for mold shoe and stacks is usually a policy matter, whether to make mold shoes or plates in house or purchase them from a mold maker supply house, either as (listed) catalogue items or have them made to order. It is essentially a simple question of economics: there are considerations, such as the shipping distance and time from a steel supplier and the need to carry steel inventories and invest much money in them. Time step QUOTING Obtain project information (part drawing, etc ) Develop rough concept Quote ORDER CLEAN UP Order received Send out order confirmation Obtain complete design information Finalize concept Quote any modifications to original concept DESIGN Stacks or inserts Mold Shoe Hot runner Assemblies BOM MANUFACTURE Inserts Process planning Programming Rough machining Hardening Final machining and polishing Shoe and Hot Runner Process planning Programming Machining (Gun drill, mill, bore and grind) ASSEMBLY TESTING Adjustments Re-testing Acceptance Prepare for shipping Shipment Sample Mold Project Timeline Figure 5.2 Time line 1281han05.pmd 28.11.2005, 11:08162 163 When selecting mold materials, there are many considerations: for the mold to last a long time and to perform best, the following characteristics must be considered for suitability:  Compressive strength  Wear resistance  Corrosion resistance  Toughness (against impact)  Thermal conductivity  Resistance to high temperature In addition to the above, the following are also very important:  Machinability  Hobbability  Polishability  Dimensional stability in heat treat  Weldability  Nitriding ability  Cost of the raw material  Availability Materials must be selected to prevent galling and seizing; materials which slide across each other should have different molecular structures (unless one of the materials is nitride plated). As a general rule of thumb, material suppliers recommend that even for dis- similar materials in a contacting condition, the difference in hardness should be 6 Rc if possible. For similar materials the difference should be 10 Rc. When selecting material for a mold, there are several material properties to be considered. The following list contains the most important properties:  Ultimate and yield strength  Impact strength  Modulus of elasticity  Hardness  The effect of temperature on these properties  Thermal conductivity  Thermal expansion  Wear resistance  Corrosion resistance The quality of the materials (cleanliness) is an important consideration. 5.1 Mold Cost and Records 1281han05.pmd 28.11.2005, 11:08163 164 5 Mold Cost, Mold Price and Delivery Some mold makers (usually larger operations) prefer to keep a selection of steels for the mold plates and for stack parts in plates and bars in their stock; this may require heavy lifting equipment, large machine tools, a large inventory, and much plant space. Other mold makers, with easy access to steel suppliers, can contract with them to supply small and large plates already cut to size, rough finished, or even ground to size. Still other mold makers (usually smaller operations) specialize in making only the stacks and to buy the completed mold shoe from mold supply houses and then to assemble and test the completed mold. In all these cases, standardization to a limited number of sizes can have a significant influence on the mold cost. Contracting large annual volumes of steel can lower the price of steel significantly. The larger the pieces of steel, and the larger the annual quantities committed to purchase from the supplier, the lower will be the cost per mass (kg). In the case of very large mold parts, it is often worthwhile to buy the steel in forgings, with only little machining allowance. The forging process incurs separate cost, but saves not only on steel costs but also on machining time. Other raw materials used in molds are BeCu, aluminum, bronze, plastics (for wear), among others. When buying BeCu, it is important to inquire before ordering how the blanks will be made. Blanks cut from rolled bars are usually free from enclosures or voids but are not available in larger sizes. If larger pieces are required, they should be pressure-cast to ensure homogeneity. It is not unusual for small voids inside the work piece to become visible after many hours had been spent on machining BeCu parts and the pieces have to be scrapped at high cost to the mold maker. Standard Hardware Today, no mold maker even thinks of making hardware items such as screws, dowels, and others. However, it is important that hardware items are used as they are provided by the supplier. Any modification can diminish their rated strength characteristics, and therefore they must not be modified for safety reasons. If they absolutely need to be modified, they must be called up in the BoM as a special part, so that they are easily identified as “special” in assembly and service. Mold Hardware Mold makers used to make many mold hardware items, such as leader pins, bushings, ejector pins, and even hot runner parts, among others. Today, it is often much less expensive to use standard hardware as supplied from mold supply houses and other specialists. They are also easier to replace for service. They are made in large quantities, on special equipment and with specially selected materials, heat treatment, and surface finishes, and are usually of much better quality than the homemade varieties. The cost of standard and mold hardware in a mold (not counting any hot runner systems) could be estimated as about 5% of the total cost. When buying steel, contract for large quantities (e.g., estimated annual requirements) for lowest price 1281han05.pmd 28.11.2005, 11:08164 165 5.1.2.3 Production Planning Cost for production planning is usually included in the overhead. It includes the costs of deciding the best way of routing the work piece through production, the selection of the appropriate machine tools, cutting speeds, the need to prepare jigs, fixtures and gages for the job (and to design them), and the cost of programming software for machining each of the required mold parts. Obviously, standardization will be of great advantage. In some CAD/CAM system, some of the programming is done as the mold part is designed. At smaller mold making enterprises, it is usually the boss or the foreman who does the production planning. 5.1.2.4 Machining Costs Machining costs includes the total of all costs incurred when transforming a “blank”, i.e., a raw piece of steel, into a finished mold part, ready for assembly. These transforming methods may include: Rough machining. Cutting blanks from rough plates, sizing and squaring these blanks, and machining these or purchased plates by milling, drilling, deep hole drilling, boring, rough grinding, or other methods. Rough turning. Rough turning from rods or cut blanks. Stress relieving. This is often required after large amounts of material have been removed (cut) from a pre-hardened work piece, which may cause it to shrink and/or warp. Stress relieving will ensure that the finished part will retain its shape after the final machining. Finish machining. Milling, drilling, turning, finish grinding, jig boring, jig grinding, honing, lapping, EDM, etc. Heat treating (hardening) (see Section 5.1.2.9) Hobbing of cavities. The method of producing cavities by hobbing is rarely used today. For details of this technology see [5]. Finishing, engraving, texturing, polishing (see Section 2.1) 5.1.2.5 Cost of Special Gages This includes the cost for any gages, fixtures, or other devices that are required to assist in machining and/or checking of this particular mold. It includes the cost of gages required to check special tapers and the cost of any special tools used to facilitates machining, which will save significant time when making any number of identical mold parts. If the cost is included in the mold cost, the customer should have the right to these manufacturing aids, but they could also be kept at the mold maker for future use for similar molds for this customer. 5.1 Mold Cost and Records 1281han05.pmd 28.11.2005, 11:08165 166 5 Mold Cost, Mold Price and Delivery 5.1.2.6 Cost of Electrodes for EDM Electrodes to produce the necessary shapes are usually machined from special carbon compounds or longer lasting, special copper alloys. For a large number of identical shapes, electrodes can also be molded or cast from special alloys by specialists in this field. Which type of material to use, or whether to use machined, molded, or cast electrodes is a question of economics and the required accuracy. In any case, the cost of making or buying the electrodes must not be overlooked; in addition, the cost of the special wire for wire EDM must be included in the mold cost. 5.1.2.7 Cost of Plating Hard chrome, flash chrome, or electroless nickel-plating and other surface finishes are best left to specialists. The cost is considered part of the mold cost. Note that if any change to a part already chrome-plated is required, the plating must first be removed (by a method similar to the plating) before re- machining. After the changes, the part must be plated again before assembly. Plating and other surface treatments are rarely done in-house. The time delay and the transport costs can be substantial and the decision maker should consider selecting a different mold material, even if it is more expensive or more difficult the machine. Typically, chrome-plating can be avoided by choosing a suitable stainless steel. 5.1.2.8 Cost of Transportation Between Shop and Service Providers Include the cost of transportation to and from specialists of any of the machining operations subcontracted by the mold maker. Operations and services performed by outsiders may include any job beyond the capacity of the mold maker’s equipment, or not within his expertise, or they may be less costly than doing them in-house. Also, the shop could temporarily be overloaded and it would be preferable to purchase the necessary service elsewhere to avoid delaying the job. The cost of transport is easily overlooked. Some mold makers consider this cost as overhead, but it should really be charged to the mold. 5.1.2.9 Cost of Heat Treatment Many mold makers use outside sources for heat treatment of the mold parts. Most heat treatment shops have regular (often daily) pickup and delivery services and this cost is usually included in the price for their service. Because the heat treatment for most mold or tool steels is different from each other and varies to achieve different hardness and toughness conditions of the steel, it is good practice for the mold designer to specify (wherever possible) 1281han05.pmd 28.11.2005, 11:08166 167 only a carefully selected, small number of different steel types and range of hardness. Occasionally, the designer can select from a small number of most frequently used “standard” steels, which can be treated to a condition almost as good as the most suitable but rarely used steel. This allows simplifying the handling of the heat treatment and shortening the time for the work pieces to be returned. Some mold makers do their own heat treatment on a selected, relatively small number of steels and subcontract only those parts that are outside the capability of their own facility, e.g., if the parts are too large for their furnaces or because it is a steel for which they have no facilities or experience in heat treating. 5.1.2.10 Cost of Inspection Inspection of mold parts between the various manufacturing steps and after completion of a part is essential. The more often the work pieces are inspected, the less is the likelihood that a “spoiled” part continues through more operations on its way to assembly, where it will be discovered to be defective. However, inspection can be very expensive. Most mold shops have their own methods and practices to minimize the cost of inspection; some have inspection stations located near certain machine tools or between the various groups of machine tools; some have central inspection stations, to avoid duplication of the usually very expensive testing equipment; some educate the machinists to check their own handiwork, some depend on independent inspectors. There is high cost incurred with checking; this could be charged to the mold cost, but it is often considered part of the general overhead. 5.1.2.11 Cost of Assembling In some mold making shops, a “lead mold maker” will do the assembly himself or supervise the assembly process by technicians or the machinists themselves, but in larger mold shops, the mold assembly is mostly done independently of the manufacturing of the mold parts. Ideally, if all drawings are correct and the parts are made to specifications, assembling a mold should not be more difficult than assembling any clean, delicate machine or apparatus. The parts are supposed to fit and nothing more than standard or torque wrenches, a soft hammer, and lubricants should be required to assemble a mold. The ancient method of fitting mold parts by filing or grinding should not be used. If parts do not fit as they should, they must be returned to the design office, to establish why they don’t fit and who was at fault: the designers, the machinists, or the suppliers. Any corrective action must originate with the responsible mold designer and be properly recorded for the future, especially if repeat orders are expected. To make changes to mold parts without this practice will only perpetuate the error. Any costs incurred should be charged against the department from which the error originated and not recorded as part of the mold cost. 5.1 Mold Cost and Records Standardize on the types of steel selected if possible Figure 5.3 Mold assembly area (Courtesy: Topgrade Molds) Inspection is expensive but saves money in the long run 1281han05.pmd 28.11.2005, 11:08167 168 5 Mold Cost, Mold Price and Delivery 5.1.2.12 Cost of Mold Testing Today, many mold makers have at least one molding machine for mold testing. If the machines in-house are not suitable for the mold to be tested, the mold maker will have to test the machines at the molder who ordered the mold. If this is too difficult because of distances and possible need for crossings of national borders (with all the problems of custom duties, paper work, etc.,) or because the customer does not want to interrupt his production just for testing a mold, the mold maker could buy machine time from a (close-by) molder. One way or another, testing a mold adds to the cost of the mold. Where and how the mold will be tested must be discussed at the time of ordering and testing time and machine time should be included in the mold cost. The actual cost of testing, i.e., the time of mounting the mold in the machine, startup, getting the mold on cycle and running it “hands-off” (i.e., without any further adjustments) for a specified length of time (typically 2–4 hours, sometimes more) and then shutting it down and removing it from the machine is only part of the test. The molded products from each cavity must be inspected for visual defects, measured for accuracy, and possibly tested for their intended performance. This of course takes time, and the mold maker may have to wait days or even weeks until the product, and the mold, is accepted. But there is also another, very important, purpose of testing: can the productivity be improved by changing molding parameters or even by changing some features of the mold or its auxiliary equipment to reduce the cycle time? This can take much longer than the planned original testing. In some cases, the customer or molder will make these tests in his own plant, after receiving the mold. An unfortunate but quite frequent result of testing is the discovery that one or more dimensions of the product are outside specifications, either in all cavities (design or concept error), or in only some of the cavities (manu- facturing or concept error). In this case, the mold needs to be removed from the machine and dismantled, the “offending” mold parts altered or replaced, or in the worst case, the mold design needs to be changed. This also means retesting of the mold. Part of a proper testing program is the issuance of a setup guide, detailing all molding parameters used for the final, nonstop test run, which pro- duced the test samples. It should be mandatory that the responsible mold designer be present during all testing procedures of “his” or “her” mold to see first hand and learn from any problems as they show up, during the installation, and the running of the mold. This person is then also respon- sible for any remedial action, for recording any problem, and to make sure that they do not occur again in the future, not only in this type of mold, but in any other mold having similar features. Even if several identical molds are made at the same time, for the same customer, they all must be individually tested. 1281han05.pmd 28.11.2005, 11:08168 [...]... relationship and trust between customer and mold maker and if the mold maker has a reputation for making good molds and for developing new, or improving existing technology In such case, the customer will readily agree to pay a quoted price for engineering and design time to develop a new mold design (or molding method) and even for any costs of prototypes and experiments, in order to arrive at a mold price. .. on the job and build a good mold Most customers understand that there is nothing gained if the mold maker is not familiar with the type of mold required I have often refused to bid and suggested to the prospective customer some other mold maker more familiar with the type of products for which he wanted a mold, not because There is a risk with every quotation 174 5 Mold Cost, Mold Price and Delivery. .. a mold- making business 180 5 Mold Cost, Mold Price and Delivery 5.5.3 “Guesstimating” the Mold Cost Because accurately calculating the mold cost is practically impossible, most mold makers use the method of estimating described in Section 5.5.2 However, there is another method that is simple and inexpensive, but quite risky, and should not be used unless with ample, long experience in the type of mold. .. independent mold maker Problems with this approach are: These molds will be more or less copies of existing technology and there will be few new ideas or improvements over the old methods so that the molder loses out on any advances in technology, which are constantly developed by independent mold makers 183 184 5 Mold Cost, Mold Price and Delivery Because the molders will be competing with mold makers,... products and mold sizes and can standardize them to such a degree to be able to even make a sales catalogue and a published price list for these molds, for example, by size of (similar) products and a certain, limited number of cavities In this case, there is virtually no risk involved at all There are many mold makers who specialize exclusively in certain molds and research ever better methods of molding... getting Ownership of the mold must be clearly established 176 5 Mold Cost, Mold Price and Delivery better productivity They invest in better and more economical methods to manufacture the mold components with shorter deliveries These mold makers specialize, e.g., in molds for bottle caps, disposable thin wall containers, toys, large pails, pallets, crates, PET preforms, small gears, and many more It is... stack parts or the mold shoe, there could still be many similarities with an older mold Machining times have also much improved over the years, with the use of CNC and There is nothing that replaces past experience, especially if the experience was bad 178 5 Mold Cost, Mold Price and Delivery automated machine tools Even though standardization and CAD/CAM has reduced the design and work preparation... Time 5.4 Mold Cost Is Absorbed by the Molder In the following, we will consider the question: Who pays for the molds? Ordinarily, a customer buys a mold from the mold maker, either directly or through the molder, at previously established price and delivery terms But there is a notable exception to this: whenever the molder has control over an in-house mold making operation, but also, if the molder must... up front for a mold, but the mold is then locked in with the molder and the customer cannot remove the mold, e.g., when planning to change the molder Also, if the molder goes into receivership, the customer must be able to prove that the mold belongs to him before being able to get possession of the mold Another, somewhat similar, scenario is when the molder has universal mold shoes and buys or makes... them, and the mold makers could be reluctant to quote or build any new molds, which the molders may require There is an exception to this: a mold making operation which is located (usually) within or next to the parent molding plant could be considered an independent organization (profit center) and will serve the molder just as an independent mold maker would, by quoting on actual costs and delivery and . this type of product or mold and has greatly 5.3 Mold Price 1281han05.pmd 28.11.2005, 11:08171 172 5 Mold Cost, Mold Price and Delivery underestimated. 28.11.2005, 11:08159 160 5 Mold Cost, Mold Price and Delivery The mold maker must make sure that only materials and times necessary for the mold as designed (originally