Is the mass production cost of robot body parts high? 3 tips for high-pressure die-casting and CNC to save you 30%

1、 Common pain points for mass production of robot body structural components

Having worked in the robotics industry for many years, we have come into contact with a large number of process engineers and procurement managers from robot manufacturers. Many of them will mention the same dilemma: how to balance cost, accuracy, and delivery cycle in the processing of robot structural components from small to medium batch to mass production?

If it is a small-scale prototype production, CNC precision parts can be directly processed using whole blanks. Although the cost is high, the advantage lies in fast delivery, controllable accuracy, and acceptable compatibility; Once it enters the mass production stage, the problems of relying solely on pure CNC machining immediately become prominent: high material costs, long machine tool occupancy time, inability to keep up with order pace, inability to lower costs, and loss of competitiveness in product pricing.

What about switching to pure high-pressure die-casting? The advantages of fast molding and low cost are indeed obvious, but the core structural components of robot precision parts processing require hole positions and installation surfaces that need to be matched with other parts. The dimensional accuracy of pure die casting cannot meet the assembly requirements, and the problems of flash, porosity, and shrinkage deformation caused by die casting result in a high defect rate. In the end, the rework cost is even higher than the processing cost, which still cannot solve the problem.

In this case, the combination process of "high-pressure die-casting+CNC machining" to complete rough forming and precision machining has become the mainstream solution for mass production robot structural parts processing. However, many factories still encounter various problems when applying this process in practice, such as excessive deformation or scrapped air holes, and the cost cannot be reduced. In this article, we will combine the practical experience of Shenzhen CNC precision machining manufacturer Huiwen Zhizao in serving robot body manufacturing for many years to compile a complete implementation guide for this process, providing reference for peer engineers.

2、 Why Combination Process is the Optimal Solution for Mass Production of Robot Body Structural Components

To clarify this issue, let's first compare the three processes of pure CNC precision part machining, pure high-pressure die-casting, and high-pressure die-casting+CNC combination from several core dimensions, in order to clearly see their respective applicable scenarios:

The difference between the three processes can be clearly seen from the above figure:

1. Material utilization rate: The combination process retains the advantages of die-casting, and the material utilization rate is more than twice that of pure CNC machining, directly reducing raw material costs from the source.

2. Production efficiency: In the combination process, die-casting is responsible for rapid prototyping of complex contours, while CNC only processes key mating surfaces, reducing processing time by 40% -60% compared to pure CNC. With the same equipment capacity, the output can be increased by more than twice, and the delivery cycle can also be correspondingly shortened.

3. Balance of precision and cost:The precision requirements for robot structural components are inherently uneven: the appearance only needs the contour to meet the design requirements, and the precision requirements are very low; However, the installation holes and positioning surfaces that match with bearings and motors require high precision and strict control of tolerances. The combination process perfectly matches this requirement: the appearance surface is directly die cast, and only CNC precision parts are machined at key positions, which not only meets the accuracy requirements but also minimizes processing costs to the greatest extent possible.

We have conducted statistics and found that for precision robot parts with an annual demand of 500-5000 pieces, using a combination of high-pressure die-casting and CNC machining can reduce the overall cost by 25% -35% compared to pure CNC machining. The defect rate can be controlled within 3%, making it the most cost-effective mass production process for robot parts under current technological conditions, especially suitable for robot body manufacturing enterprises to reduce costs and increase efficiency.

3、 Deep analysis of the three core difficulties in the combination process

Many processing plants can do high-pressure die-casting and CNC precision parts processing, but why is the stability of the composite process parts always poor? We have summarized more than ten years of production experience in robot body manufacturing and found that the core problem lies in the control of three difficult points. As long as these three points are done well, the yield rate can be improved.

1. Internal stress and deformation control of die-casting blanks

This is the most common problem with the combination process. Many factories start CNC machining directly after casting the blank and leaving it for one or two days. During the machining process, the dimensions are measured correctly, but after a week of testing, the dimensions exceed the tolerance. The root cause is that the internal stress of the die-casting blank has not been fully released.

During the high-pressure die-casting process, the high-temperature metal liquid rapidly cools and solidifies, and the cooling rate varies at different positions of the parts, resulting in significant residual internal stress; After die-casting, the blank is taken out of the mold, and temperature changes will further generate internal stress. If the internal stress is not released before cutting, after removing some of the material, the internal stress balance will be broken and redistributed, resulting in bending and warping deformation of the part, and the final size deviation from the tolerance.

Regarding this issue, Huiwen Zhizao has summarized two mature control schemes in long-term practice, and the comparison is as follows:

We have conducted comparative tests and found that the size change of the blank without sufficient stress release after one week of processing is 3-5 times that of the blank with sufficient stress release. Adequate stress release can stably control the deformation within the tolerance range required by the customer, avoiding subsequent size deviation and scrap.

2. Clamping and positioning design for irregular blanks

Die cast blanks are formed in one go. Compared with forged blanks and rolled blanks, they have larger dimensional tolerances and more irregular contours. Many factories are accustomed to using universal fixtures to clamp them, either because they are not tightly clamped and cause machining displacement, or because the clamping force is too strong and causes deformation of the blank clamp, ultimately affecting machining accuracy.

Clamping and positioning are the foundation of CNC precision part machining. If the positioning is inaccurate, the subsequent machining accuracy cannot be discussed at all. Our experience is that customized tooling design is necessary for the clamping problem of die-casting blanks. There are two core ideas：

1. Prioritize using the forming reference of the die-casting blank as the positioning reference, such as the parting surface and gate position of the die-casting mold, which are the reference of the blank itself. Using these positions for positioning can reduce the impact of blank errors on machining accuracy;

2. Customized soft claws or imitation fixtures: Soft claws are made according to the outer contour of the blank, with a reserved adjustment of 0.03-0.05mm. The clamping force is controlled within a reasonable range, ensuring stable clamping and preventing deformation of the blank due to excessive clamping force.

For example, let's take a practical production case: the upper arm connecting arm of a six axis robot body has an irregular contour of the die cast blank. Initially, it was clamped with a universal three jaw fixture, and after processing, the hole position tolerance exceeded the tolerance rate by 12%. Later, we customized a contour shaped soft jaw based on the outer contour of the blank, optimized the clamping force parameters, and directly reduced the tolerance rate to within 1%, with a very significant effect.

3. Prevention and Control of Gas Hole Defects in Die Casting

During the high-pressure die-casting process, molten metal is injected into the mold cavity at high speed, which can easily draw in air and form subcutaneous pores inside the blank. If the pores happen to appear on the mating surface of CNC precision machining, they will be exposed after processing, directly leading to the scrapping of the parts. This is also one of the main reasons for the low yield of composite processes in many factories.

To solve the problem of porosity, it is not enough to rely solely on selection after processing. Prevention must start from the process design stage. We have summarized three control steps:

1. Structural optimization: In the process pre evaluation stage, we will communicate with the customer's design engineer and suggest reserving process holes in thick walled areas that are prone to porosity, or adjusting the wall thickness to reduce the probability of porosity; If porosity is unavoidable, reserve sufficient machining allowance to allow porosity to be removed through machining;

2. Optimization of Die Casting Process: Collaborate with cooperating die casting factories to adjust die casting parameters, optimize the position of the inlet gate and the design of the exhaust groove, so that the air in the mold cavity can be fully discharged and the generation of air holes can be reduced; For parts with high requirements, vacuum die casting technology is used to further reduce the occurrence rate of porosity;

3. Processing process inspection: After rough machining is completed, conduct a visual inspection first to confirm that there are no exposed pores on the precision machined surface, and then perform precision machining to avoid wasting subsequent processing time on scrapped parts and reduce ineffective production costs.

Through these three controls, we have now controlled the porosity scrap rate of the combined process within 1%, which is much lower than the industry average and effectively reduces the comprehensive production cost of robot body manufacturing.

4、 Detailed explanation of standardized process flow for combination technology

Based on years of production experience, Huiwen Zhizao has developed a standardized process for high-pressure die-casting and CNC precision parts processing of robot body structural components. Each link has clear process requirements to ensure the stability of different batches of products. Here, we share with you:

Step 1: Pre evaluation of Process Feasibility

After receiving the customer's drawing requirements, we first conduct a feasibility assessment of the process: evaluating whether the structure, batch size, and accuracy requirements of the parts are suitable for using a combination process, and providing optimization suggestions to the customer, including blank allowance reservation, tolerance allocation, structural optimization, etc. For example, some parts designed by customers have large local wall thickness differences, which can easily lead to porosity and deformation. We will provide structural adjustment suggestions from the processing end to help customers optimize the design and reduce subsequent production difficulties and costs.

Relying on the integrated capability of "design+manufacturing+assembly" of Huiwen Zhizao, we can provide customers with full process process process support, without the need for customers to connect with die-casting factories and CNC machining factories themselves, reducing communication costs.

Step 2: Production and factory inspection of die-casting blanks

The die-casting suppliers we cooperate with all have IATF16949 automotive grade quality management qualifications and strictly produce according to the raw material drawings and process requirements we provide. The raw materials will undergo preliminary inspection before leaving the factory, and will only be sent to our Shenzhen factory after passing the inspection. After the raw materials enter the factory, we also need to conduct an incoming inspection: sampling the size, hardness, and internal defects of the raw materials. Unqualified raw materials are directly returned to avoid flowing into the next process.

Step 3: Stress Release Treatment

The qualified raw materials, according to our process requirements, enter the natural aging zone or vibration stress relief process to complete the release of internal stress. No matter how tight the delivery time is, this step will not be omitted because it is the core foundation for controlling subsequent deformation.

Step 4: CNC precision machining of parts

After the stress release is completed, it enters the CNC machining process. Huiwen Zhizao has a 10000 square meter factory and 200+processing equipment in Shenzhen, with the ability to continuously process multiple processes. It can complete milling, drilling, boring, reaming and other machining tasks on multiple surfaces in one clamping, reducing positioning errors caused by multiple clamping and ensuring machining accuracy.

Step 5: Post processing and Finished Product Inspection

After processing, deburring and surface treatment (anodizing, sandblasting, etc., according to customer requirements) should be carried out first, and then the finished product inspection process should be carried out. All key dimensions must be fully inspected, and the inspection data should be recorded and archived. Only after passing the inspection can they be packaged and stored for shipment.

The entire process, from raw materials entering the factory to finished products leaving the factory, has clear process documents and inspection standards at each stage, ensuring stable and consistent quality regardless of which batch is produced.

5、 Full process quality control system guarantee

As a high-end robot full industry chain service provider specializing in the field of robotics, Huiwen Zhizao is a national high-tech enterprise and a specialized and innovative enterprise. It has passed ISO9001 and IATF16949 quality management system certifications and established a comprehensive quality control system for CNC precision parts processing：

1. Professional testing equipment: equipped with professional testing equipment such as coordinate measuring instruments, roughness testers, height gauges, etc., to meet the testing needs of parts with different accuracy levels;

2. Archive of testing data: All finished product testing data will be archived and traceable. If customers have future needs, they can retrieve the testing report at any time.

Based on the technical background of the Chinese Academy of Sciences, we have been deeply involved in the field of robotics for a long time, making quality control an important part of production. We have served many listed companies and industry leaders, such as Lenovo, Xinsong, Xiaomi Ecological Chain, and Beijing Institute of Technology, with a batch delivery qualification rate of over 98%.

6、 Frequently Asked Questions and Answers

Q1: What is the appropriate batch size for high-pressure die-casting and CNC precision parts processing?

A: Generally speaking, if the annual demand for a single variety exceeds 500 pieces, the cost advantage of using combination technology will be reflected; If the annual demand exceeds 1000 pieces, the comprehensive cost advantage will be very obvious. If it is a prototype with dozens of pieces, the cost of opening the die-casting mold will increase the total cost, making it more suitable for pure CNC machining.

Q2: Which materials are suitable for this combination process?

A: The most commonly used structural components for robots are aluminum alloys, such as ADC12 and A356, which are very suitable for high-pressure die-casting+CNC combination processes. Zinc alloys can also be used. Currently, the aluminum alloy robot structural components we produce the most are aluminum alloy.

Q3: How much tolerance can the combination process achieve?

A: According to the different sizes and structures of the parts, the dimensional tolerances of the key mating surfaces can reach IT7-IT9 levels, meeting the assembly requirements of the vast majority of robot body structural components. If there are higher requirements, we can adjust the process to meet the special needs of customers.

7、 Summary

The combination process of high-pressure die casting and CNC precision part processing is currently the most cost-effective process solution for mass-produced robot structural components. Its core value is to effectively reduce comprehensive production costs and improve production efficiency while ensuring accuracy requirements. The core of this process lies in three key points: sufficient stress release and deformation control of the die-casting blank, customized fixture positioning to ensure machining accuracy, and prevention of porosity defects from the design end. As long as these three points are done well, qualified parts can be stably produced.

Huiwen Zhizao has long been deeply involved in the field of robot body hardware, focusing on the full industry chain services of robot mechanical design, core component manufacturing, assembly, etc. We provide robot body hardware design and manufacturing services, covering the entire process of design (mechanical structure/electrical scheme design/process optimization), manufacturing (CNC machining/mold/surface treatment), assembly (component trial assembly/product assembly and debugging), and supporting customers to choose single or multiple service modules as needed.

In the field of high-pressure die-casting combined with CNC precision parts processing, we currently innovatively adopt the combination process of "new materials+new molds+precision machining", relying on the integrated full chain service of design, intelligent manufacturing, and assembly. We have the ability to provide one-stop service from research and development to batch delivery, and can help customers solve various problems in the process implementation. In addition, in terms of OEM business, Huiwen Zhizao can undertake customized processing of various types of structural components such as humanoid robots, quadruped mechanical dogs, flexible robotic arms, bionic robots, medical robots, etc.

If you are developing a mass production robot project and need to find a professional robot parts processing service provider, please feel free to send us drawings for consultation. We will provide you with professional process solutions and quotation services.