Current mold market is affected by rising raw material prices, increased labor costs, and fluctuations in international trade, making mold profit margins smaller and smaller. How to maximize profit of mold and realize green manufacturing while obtaining orders in fierce market competition is a problem that every mold enterprise is thinking about. Injection mold manufacturing cost control is imperative, cost control lies in effective spending, not ineffective savings.
In process of mold manufacturing, mold management can be divided into schedule and delivery management, quality management, cost management, technology and talent management, after-sales management, among which cost management is key factor affecting mold profits. Mold manufacturing cost is mainly composed of material cost, design cost, processing cost, assembly cost, mold trial cost, transportation cost, maintenance cost, quality cost, progress cost, management cost, etc., as shown in Figure 1.

 

Figure 1 Main components of mold manufacturing cost
Cost control requires participation of all staff. Development of cost awareness among mold workers requires continuous promotion and penetration of corporate culture, strengthening cost awareness training, and gradually establishing staff awareness of "cost" and "benefit". Cost control in mold design stage is core of the entire mold manufacturing cost control. Mold design is the first step in mold manufacturing. Importance of cost should be emphasized in design process to improve designer's sensitivity to cost. Following introduces control method of injection molding manufacturing cost from aspects of budget control and process control.

Quotation department makes "Mold Manufacturing Cost Budget" (see Table 1) according to mold contract, and design department evaluates each link according to "Mold Manufacturing Cost Budget" in mold making cycle, fills in "Design Change Budget Sheet" when budget is exceeded, promptly informs project and person in charge of sales department to communicate with customer, and at the same time changes "Mold Manufacturing Cost Budget Sheet" to achieve purpose of order value-added. Specific process is shown in Figure 2.
Table 1 Mold manufacturing cost budget

 

 

Figure 2 Comparison of each link and mold budget
(1) Finalized cost control link. Person in charge of design shall control mold size within budget according to requirements of "Mold Manufacturing Cost Budget Table" during finalization meeting.
(2) Design link. Person in charge of design shall check cost according to "Mold Manufacturing Cost Budget Table", and evaluate whether mold opening data is same as quotation data.
(3) Cost control link in customer review process. Evaluate whether customer has requirements such as increasing size of mold and adding related spare parts during review process.
Design department summarizes all "design and change budgets" in month and forms a "mold design and change list summary table" (see Table 2), and sends it to project department for follow-up before the first mold trial of month, and project department reports results to design department.
Table 2 Summary table of mold design and variation list

(1) Pre-job training for new employees to familiarize them with company's processes, standards, machine tools, processing methods, and tool use methods as soon as possible.
(2) By regularly organizing different forms of internal technical exchange activities, providing a communication platform for technical personnel, sharing experience of technical personnel in work, and improving comprehensive ability of team.
(3) Encourage technicians to participate in or hold skill competitions to stimulate their self-learning ability and improve their personal skills.

Inventory materials are divided into safety stock materials and dead stock materials. Safety stock materials are enterprises that purchase a certain amount of emergency materials in advance in order to solve problem that material delivery time cannot meet requirements of mold manufacturing progress, which are generally industry standard parts or enterprise standard parts. In addition to delivery time, materials purchased in bulk by enterprise due to price advantage of centralized procurement are also classified as safety stock materials. Under normal operation of enterprise, backlog of inventory funds is controlled within a reasonable range. Dead stock materials refer to materials generated due to some design changes, manufacturing or purchasing exceptions, and these materials have reuse value.
Effective use of safety stock materials: After design engineer completes BOM design, it is automatically associated with warehouse system according to identification code, specifications and models are automatically matched from safety stock list. Effective use of stockpiled materials: Design engineers search for stockpiled material information in design stage, consume stockpiles in real time through scheme design, and activate funds.

To establish a sound and scientific quality assurance system, quality inspectors should be familiar with customer standards and parts acceptance requirements, and control costs under premise of ensuring quality.
(1) Quality department conducts a full inspection of all incoming materials in strict accordance with requirements of drawings.
(2) Quality department shall inspect quality of parts in process strictly according to requirements of drawings, and deal with problems of each link in time.
(3) Establish a quality management ledger to record each quality anomaly and cause analysis.

Project department is responsible for sharing of product information, such as product mass production, product appearance requirements, precision requirements, special mold requirements, and product assembly relationships. Purchasing department shares unit price and delivery cycle of materials, such as steel price, delivery cycle of different materials, brand standard specification material size, etc. Information sharing facilitates design scalability.

Based on "Mold Manufacturing Cost Budget Table", combined with customer standards and reference drawings, size of mold plate is preliminarily determined, design person in charge will review and check; at finalization review meeting, mold strength will be jointly evaluated with process and mold making personnel, as shown in Figure 3 shown. Notify project and business department when budget is exceeded, so as to obtain concessions or additional costs from customer or take other remedial measures, such as optimizing structure and selecting materials reasonably, to ensure that the overall manufacturing cost of mold is controlled within budget.

 

Figure 3 Die strength analysis

Designers and programmers review processing technology of drawings and determine final processing methods and ideas. Programmers formulate different processing parameters and select tools according to machining accuracy of mold parts, so as to improve processing efficiency and reduce processing costs on premise of ensuring quality. In design stage, processing technology of parts is planned, and designers understand processing capabilities of factory machine tools. Parts with little difference in material, size and shape should use splicing process as much as possible, as shown in Figure 4.

 

Figure 4 Splicing processing
Non-glue side side R angle is designed according to "safe processing depth" in Table 3. In special cases, it is designed according to "maximum processing depth". The larger side R angle, the better processing.
Table 3 Tool parameters

When non-adhesive bottom surface is flat, R angle of bottom surface can be 0, that is, it is designed to be a sharp corner, but it is better to design a rounded corner of R1 mm or larger, as shown in Figure 5(a). When bottom surface of non-adhesive position is not flat, side surface should be designed as an inclined surface, slope should be ≥3.5°, R angle of bottom surface should be as large as possible, and dimensions should be as few as possible, so that same tool can be used for processing, as shown in Figure 5(b) .

 

Figure 5 Design of R angle of non-adhesive plane
Size of trapezoidal runner should be designed according to existing tool, diameter of circular runner should be designed according to size of ball cutter as much as possible to improve processing efficiency. Parting surface and avoidance surface of mold should be designed as flat as possible to avoid dead corners that cannot be processed by CNC. Process is refined to each step, processing benchmark and clamping position of each step are designed in advance to reduce number of processing and clamping as much as possible, as shown in Figure 6.

 

Figure 6 Parts Machining Benchmark
According to precision requirements of mold parts, design intention is correctly communicated to programmer in a 3D color management method, as shown in Figure 7, to improve processing efficiency.

 

Figure 7 3D color management
The whole pair of molds is composed of different parts, especially complex structure of slider and lifter. It is necessary to perform motion simulation in advance to prevent interference, ensure stable and reliable mold assembly and movement, as shown in Figure 8.

 

Figure 8 Schematic diagram of movement of lifter assembly

Large mold material is determined on the basis of "Mold Manufacturing Cost Budget Table", and small mold material is reasonably selected in combination with customer standards and company standards. When customer reviews higher material requirements to meet certain requirements (such as service life, cooling efficiency, etc.), project and business department should be notified in time to charge customer with additional costs. Secondly, when it is impossible to make additional fees to customer due to error in quotation due to deviation of understanding of customer's needs, other remedial measures should be adopted to ensure that the overall manufacturing cost of mold is controlled within budget.

Hot runner accessories are subject to "Mold Manufacturing Cost Budget", and other standard parts are subject to customer design standards or technical agreements. As far as possible on the premise of meeting performance requirements of mold, with consent of customer to replace original imported standard parts with domestic standard parts, as shown in Figure 9. Reasonable optimization of mold design scheme, such as changing hydraulic cylinder core pulling to mechanical core pulling can avoid use of expensive standard parts (hydraulic cylinder, diverter, etc.), optimize gating system to reduce number of hot nozzles, etc. When customer proposes a design change request exceeding budget during review process, project and sales department shall be notified in time so that customer can be additionally charged.

 

Figure 9 Commonly used standard parts for molds

Use expert-level mold rapid design tool based on standardization and modularization to realize full 3D automatic design and improve design efficiency, as shown in Figure 10.

 

Figure 10 Digital Design Tools

(1) Production schedule. First, evaluate processing time according to simulation time of program process sheet and consider clamping time of workpiece, then reasonably allocate machine tool processing according to requirements of program process sheet and performance of machine tool, and give full play to advantages of machine tool to improve utilization rate of machine tool.
(2) Automatic programming is preferred. Deep hole drilling process adopts automatic programming. As shown in Figure 11, the total monthly cost can be automatically calculated through connected computer. Through these data, deep hole drilling process price of same type of mold and utilization rate of machine tool can be evaluated.

 

Figure 11 Example of automatic programming of deep hole drilling

(3) 3D automatic detection report. One-click generation of point features according to 3D digital model, automatic programming according to planned inspection scheme, and automatic generation of a 3D inspection report after inspection is completed, as shown in Figure 12, engineers can view it directly in 3D software or browser, which improves efficiency of parts inspection, reduce duplication of work.

 

Figure 12 Automatic detection

Principle of material procurement cost control is to ensure that project material cost is within scope of mold manufacturing cost budget, and to reduce procurement cost as much as possible on premise of ensuring quality. Person in charge of purchasing checks cost according to "Mold Manufacturing Cost Budget Table", evaluates whether purchase price exceeds budget, and reports to design department if it exceeds. Material procurement cost control measures are as follows.
(1) Avoid expedited procurement, and plan ahead for materials with long procurement cycles.
(3) On the premise of ensuring product quality, through bulk procurement, suppliers are required to send them to different warehouses, rational use of resources, and reduction of procurement costs.
(4) Quality department and purchasing department seek high-quality, long-term cooperative standard parts suppliers.

Cost control measures in mold trial stage are as follows: ① Reasonably arrange mold test machine tools, and build a mold test environment as much as possible according to mold mass production requirements, such as water, oil, gas connections, etc., as shown in Figure 13; ② Strictly control number of mold trials to reduce cost of mold testing; ③Test mold according to parameters of mold flow analysis report, as shown in Figure 14, to improve efficiency of mold trial; ④ Process parameters of final injection-molded qualified products are verified by mold flow analysis again by engineer, reasons and analysis are recorded at the same time, added to mold flow analysis database as a reference for next production of same type of products.

 

Figure 13. Injection molding machine try-out simulation matching

 

Figure 14 Mold Flow Analysis Report

After mold is delivered, professional cost accounting personnel will calculate cost, and organize person in charge of each mold process and person in charge of quotation to conduct a summary meeting, compare with original quotation, summarize cause of problem and preventive measures, and provide same type of follow-up manufacturing. When making molds, we can quickly give reasonable quotations according to market dynamics.