Mold Cost, Mold Price and Delivery

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 Keep proper records of any job! Major costs to make a mold: Raw materials Direct labor (hours) Machining costs (hours) Purchased components Equipment depreciation Testing costs (hours) Overhead Plant costs (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 towork with an often unwieldy, large drawing. 160 5 Mold Cost, Mold Price and Delivery Always create job files for every project (molds, etc.) 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 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 For multi-cavity molds, a rule of thumb is toorder 5% spare parts and round up 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 goodpractice 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. 5.1 Mold Cost and Records 161 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 (ComputerAssisted Design) has revolutionizeddesign 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. Figure 5.1 Mold designer working at a CAD station 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. From experience, it is practically impossible to check one’s own designs and drawings 162 5 Mold Cost, Mold Price and Delivery Figure 5.2 Time line Sample Mold Project Timeline 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 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. 5.1 Mold Cost and Records 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. ... - tailieumienphi.vn