Mould industry is the basic industry of national economy. Mould is the basic process equipment for military industry, machinery, electronics and light industry. With the development of production and science and technology, the intensifying competition in the economic and trade market promotes the accelerated updating and upgrading of products, which puts forward higher requirements on the quantity, quality, cost and delivery time of moulds. The key of mould development lies in design. It can be said that this is the consensus of our industry, many units have this feeling – not afraid of processing, but afraid of design. It can be seen that a mold is much more difficult to design than to process. The author believes that a successful mould can not only complete the scheduled stamping task, but also minimize the total cost of the mould in a series of processes such as processing, adjustment, maintenance and wearing parts consumption, which is the highest limit of mould design.
Methods of reducing mould cost
The cost of mould mainly consists of the following parts: material cost, design cost, processing cost (including commissioning cost), packaging cost and transportation cost, tax and other costs (such as commercial operation and management fee). The total of material cost, processing cost and tax shall account for at least 80% of the total cost of mould. However, the material cost and processing cost are determined by the design drawings, what brand of materials to be used, how much raw materials to be used, what process route to be adopted for processing of die parts, whether good debugging performance is provided, and how many modifications are made, all of which depend on the design. Therefore, die design is the most critical link. Therefore, the mould cost shall be controlled from the design. To achieve the purpose of cost reduction, the following work shall be done in summary:
First of all, the overall design scheme shall be reasonable, that is, the design concept shall be correct, and the determination of stamping process, layout and overall structure shall comply with relevant principles or rules. For example, according to the conventional design rules, the first step is to punch out the guide hole first, and then the second step must be set to guide the guide pin. No matter how small the step distance is, it cannot be opened. If not so arranged, the initial feeding accuracy and the whole die step distance accuracy cannot be guaranteed, which means that the positioning reference is lost, and the accuracy of the stamping parts is not covered.
How to effectively control the blanking, bending, drawing, folding and hemming processes of strip, and how to use the structure to ensure that the blank is formed according to the design intent. The formulation of these schemes requires designers to have a full understanding of the deformation law of materials. At the same time, necessary check and calculation shall be carried out for the current scheme, such as the size of the spread size, the determination of the number of drawings, the value of the initial clearance, the deviation position of the pressure center, the size of the pressing force, the unloading force or the pushing force, the length of the spring and the compression amount, etc. shall be calculated first and used as the theoretical basis for the design. Mature structure shall be adopted as far as possible.
When designing the die structure, it is better to imagine the future assembly and operation of the die and the deformation process of the strip. In this way, many unrealistic assembly problems or interference generated during operation can be found in advance, and problems such as blocking feeding and unstable positioning can be solved from the beginning of the design. Because once a big design error occurs, the die will be scrapped. The author has ever seen such a pair of mold, its last station to complete cutting, 87 ° bending, the three actions of cutting out, sample layout is not wrong, because the structure design has not taken into account, only meet the requirements of acute angle bending, but the swing male mold set the lower baffle block the discharge of the production parts, cannot work continuously, a problem that is easy to deal with has been complicated, finally the mold has been scrapped. Later, the structure of the new mold was changed, the convex mold was changed to straight-through type, the concave mold was changed to bevel, and the mold was accepted after the baffle was removed. Therefore, there must be no major problem in the overall scheme.
Before determining the stamping process route and layout, the cost of various schemes is estimated, which can provide the basis for decision-making. For example, a stamping part can be stamped with several sets of single-step dies, or with one set of jump die (step die). It can also be stamped with a composite die. What scheme should be adopted and the minimum comprehensive cost should be compared.
Implement the promotion and application of standard parts and use standard parts as much as possible. This is simple because standards can be produced in series, so their market prices are relatively cheaper. Another advantage is that the mould manufacturing cycle is shortened, reducing the total workload by at least half. At present, there are a lot of mold standard parts in the market, with various types and complete specifications. For example, spring, die holder, guide, screw plug, guiding hole convex die and female die, guiding pin, inspection pin, small pressing plate, floating material pin, ejector pin, etc., these parts can be purchased from special manufacturers, thus eliminating design and processing work. It reduces the pressure on the production link, accelerates the progress, and in turn plays a certain role in promoting sales.
Process review of non-standard parts design shall not be ignored. In actual production, the cause of parts scrapping is sometimes not the operator, but the unreasonable design. For example, if a plate with a value of thousands of yuan is scrapped due to the crack of a sharp corner of the molding hole, can the responsibility be transferred to the heat treatment? Because the wall thickness of the female die insert is too weak, after cutting the forming hole, it will deform and be scrapped, which can blame the slow threading operator? In addition, if a complex special-shaped hole is designed to be spliced, the machining of male and female dies is much easier, and the tool grinder can ensure the dimensional accuracy requirements. If the hole is designed as a whole, it must be processed with a slow thread or coordinate grinder, resulting in a processing cost of hundreds of thousands of yuan. Sometimes, the punch is too thin and the impact resistance is too poor, resulting in frequent shutdown and maintenance and replacement in the stamping production, increasing the cost and delaying the production. The phenomena described above are often encountered. Therefore, for non-standard parts, process review must be carried out before production, and senior designers or technologists shall check whether the drawings meet the process conditions of the factory. If the dimension cannot exceed the maximum stroke of the existing equipment, the datum shall be kept consistent all the time, the curve (surface) processing shall avoid interference, the sharp angle easy to crack during quenching shall be avoided, the clamping surface shall be large enough, the dimensional accuracy and form and position tolerance shall be easy to control, and the modification margin shall be reserved for some parts that cannot be designed and finalized at one time. With process review, many additional costs due to unreasonable design can be reduced, thus reducing plant losses. For the purpose of clear division of work and convenient management, some enterprises divide the design work from the process preparation work, and each is responsible for its own, so the internal consumption is relatively large.
Materials shall be selected appropriately. Now people have realized the value of resources, the price of mould raw materials rises again and again, especially the alloy tool steel, some prices have exceeded the original two times. For example, the original price of high-speed steel W6Mo5 Cr4V2 was less than 40 yuan/kg, but now it rises to more than 80 yuan/kg. The original price of cemented carbide YG15 is 300 yuan/kg, and now it rises to more than 700 yuan/kg. The price of imported materials is even higher. For example, the price of common mould steel SKD11 in Japan is 70 yuan/kg, that of cemented carbide D30 is 3000 yuan/kg, and that of cemented carbide CD650 in America is 3000 yuan/kg, more than 3 times higher than that of domestic materials with the same performance. Therefore, as long as the die material can meet the performance conditions such as strength and hardness of the parts and reach the expected life, the cheap raw materials shall be used as far as possible, while the expensive materials are blindly pursued. It seems to improve the quality of the die, in fact, it is the unreasonable use of resources, which is also a waste. Domestic mould materials such as T8 T10, CrWMn, Cr12MoV, etc. are much cheaper, so it is recommended to give priority. Especially when the mould size is large, the material selection should be more careful. If some key parts must be made of wear-resistant hard alloy materials such as YG15, they can be designed in the form of hot inlay or partial welding. Try to reduce their consumption as little as possible, so as to save a lot of money.
Before leaving the factory, the mould must be subject to trial punching for several times, and the problems found in each trial mould shall be modified and thoroughly solved in the factory. It is better to debug the mould to the extent of stability before packaging and delivery. It is very difficult to repair or transform the mould by bench worker only because there is no professional equipment and operator on site to cooperate after the mould is transported to the user. Waste of time and increase of expenses are the second. If the mould is not well prepared, it must be transported back to the factory for repair, which will be more troublesome. These costs will certainly exceed the budget. At the same time, the production progress of users is delayed, causing negative impacts. In a word, the time and workload of mould adjustment shall be minimized.
The design of drawings shall be standardized. The actual size of the graphics on the computer must be strictly consistent with the marked size, and the naming shall be unique. The name and drawing number shall not be repeated. This may seem troublesome and slow, but it can bring great convenience to the subsequent series of work. The drawing file can be directly called from the computer no matter it is checked, processed, programmed or checked. Ensure that the design drawings have a clear guiding effect on production. In general, it not only saves a lot of time, but also improves the accuracy rate of dimension and shape expression, which can effectively avoid scrap or repair caused by misunderstanding of others, and effectively reduce unnecessary losses and waste.
Conclusion:
A series of relevant systems shall be established to guarantee the implementation of the above items. In this way, the mould design and development level and benefits of enterprises will be significantly improved.
