Stamping is one of the four major processes in automobile manufacturing. The manufacturing accuracy of the car body largely depends on the precision of stamping and its assemblies. Stamping technology originated from the development and demand of mass production, especially the growth of the automotive industry, and this remains true to this day.

The current development status of automotive stamping technology in China is reflected in the following aspects.

High Level of Automated Production for Outer Body Panels

Outer body panels have stringent surface quality requirements and can only be produced by automated lines. Although the automated production of automotive outer body panels in China cannot be classified as high-speed stamping, its automation level is fairly high, mainly reflected in the widespread adoption of automated linked stamping lines.

A linked stamping line generally consists of 4 presses forming a complete closed stamping line. Robots perform automatic material feeding and part retrieval in between, with a production rhythm of approximately 10~15 strokes per minute. A typical configuration includes a first double-action 1630T press followed by 800T presses.

Automatic or Semi-Automatic Production for Inner Body Panels such as Floors and Roofs

The production mode for such parts is mainly determined by production volume, generally adopting automatic or semi-automatic production. Except for joint ventures, local enterprises mostly started with semi-automatic stamping.

Semi-automatic stamping imposes specific requirements on presses. First, the press table must be large. Second, due to high forming force, the first press needs to be 2000T or 2400T, and subsequent presses no less than 1000T or 1250T.

Chassis Structural Components Mostly Manufactured by Component Suppliers

Chassis structural parts are mostly produced by component suppliers and then delivered to OEMs. Large-scale component manufacturers usually operate 6 stamping lines. To facilitate quality control and production logistics management for OEMs, these component companies are equipped with welding and even subsequent painting or coating processes, enabling them to supply finished assemblies directly to vehicle manufacturers.

Rapid Development of Precision Stamping Technology

Originated in Switzerland alongside the watchmaking industry, precision stamping is one of the key technologies for automotive industry development. It is widely applied in the manufacturing of certain automotive assemblies such as door hinge assemblies and window regulator assemblies. These parts have a material thickness of 3–5 mm and demand high dimensional accuracy, good strength, and smooth and reliable assembly operation.

After years of development, precision stamping technology has achieved gratifying results in China’s automotive industry. A number of powerful precision stamping enterprises have emerged domestically.

Development and Application of Main Stamping Processes and Hydroforming Technology

The mainstream stamping process in China still adopts the linear die production mode. As for special forming processes such as hydroforming, while related introductions and reports are common, most developments remain in the laboratory stage.

Industrial hydroforming technology is mainly used for tubular part forming. Overseas, it is mostly applied to low-volume custom automotive component manufacturing. At present, it has not yet been applied to body panel forming in China.

Hydroforming has prominent advantages:

1. In principle, it is isostatic forming, relying on high-pressure medium to deform sheet metal. The sheet is under normal compression in a triaxial stress state, which improves local forming performance and facilitates forming of more complex body panels.
2. Its forming principle and liquid medium replace the traditional steel-to-steel contact forming method, effectively reducing sheet scratching and greatly benefiting surface quality improvement.
3. It relaxes the restrictions on stamping forming directions imposed by conventional stamping.
4. Multiple forming operations can be completed in one step, helping reduce working procedures and the number of dies.
5. Work hardening during forming helps increase the strength of finished parts. Meanwhile, overseas application shows its production cycle is not slow.

Nevertheless, hydroforming also has drawbacks. Its application limitations are obvious: it requires external liquid medium and corresponding equipment. Post-processing of parts is necessary prior to welding. Considering its impact on on-site working environment, it is not suitable for mass production.

Existing Problems in Domestic Automotive Body Panel Die Manufacturing

Automotive body panels are divided into inner and outer panels, and correspondingly there are inner and outer panel dies. For inner panels, major surface quality issues include springback and distortion. Stable and reliable dies mainly prevent galling and reduce part warpage and deformation. For outer panels, surface defects mainly involve scratches, burrs on holes and edges, local depressions, forming quality of mating surfaces, and assembly gaps after component fitting. The dies require exquisitely machined working sections, precise assembly and smooth die movement.

China has fully acquired the capability and technology to manufacture complete body dies for mid-range passenger vehicles. However, dies are custom single-unit products. Regardless of the die manufacturer, each set of dies is ultimately designed and fabricated by specific engineers. Although much can be done to accumulate overall experience and promote standardization, since dies are produced in single batches, final quality still largely depends on individual expertise.

Currently, domestic OEMs mainly source inner panel dies from domestic manufacturers, while some critical outer panel dies are outsourced. Outsourcing stems from richer overseas experience; clients expect better manufacturing cycles and quality. In fact, outsourced dies also have many defects, yet clients tend to perceive more problems with domestically made dies.

In summary, automotive body panels feature large dimensions and are produced via linked production using linked dies. Multi-station progressive dies are widely used abroad for small and medium stamping parts with high efficiency. With continuous growth of China’s automotive industry, the domestic automotive die sector keeps advancing. The competitive edge of foreign die makers will gradually weaken, and domestically manufactured dies will gain wider recognition over time.

Expectations for Improved CAD/CAE System Integration Technology in Automotive Stamping Die Design

When discussing automotive stamping technology, automotive stamping die design cannot be overlooked.

Compared with ten years ago, mainstream CAD/CAE systems on the market have undergone tremendous changes. Previously generalized systems have been adapted and redeveloped for practical die manufacturing, representing substantial progress.

Some typical CAD/CAE systems available today have powerful functions. However, in practical application, expected outcomes are often not fully achieved due to varying operating conditions, with several unsatisfactory aspects. In the long run, from the perspectives of cost reduction and service, powerful domestic CAD/CAM systems would be highly desirable.

CAD/CAE integration will become an inevitable demand and trend in the long term. Many attempts have already been made, yet the practical application effect remains unsatisfactory.

CAD/CAE systems need to systematically sort out, analyze and feature-encode the design logic for body panel dies, and then find integration points at the software level. Thinkdesign is outstanding in this regard; it can accurately realize engineers’ intentions for springback compensation.

Integration between different software systems keeps advancing. Physical networking is no longer an issue, and some die factories have realized CAD/CAM integration under the PDM environment. However, looking at the relationship between system development and industrial application by die makers, mature experience can only be accumulated through industrial use. Die makers need investment for adoption, and investment requires returns. Talent training is also an unavoidable challenge.

Machine Tool and Cutting Tool Requirements for Automotive Stamping Die Manufacturing

1. Requirements for Machine Tool Equipment

The core requirements for equipment in automotive stamping die manufacturing lie in stability and reliability.

The author recently visited a die enterprise. Its staff mentioned the performance of several existing machines and a newly installed machining center, emphasizing that precision retention of equipment is critical. They also pointed out that modern equipment relies increasingly on the skills and professionalism of installation technicians. Technicians must properly install and commission equipment to optimal status. During operator training, key points of equipment operation and maintenance together with their consequences must be stressed.

Die manufacturers have high expectations for their high-value equipment. Joint efforts from all parties are required to meet preset targets and achieve win-win results. It would be ideal if equipment suppliers conduct regular user visits, on-site services, and even overhaul and retrofitting services.

2. Requirements for Cutting Tools

As previously discussed, cutting tool requirements are mainly as follows: ① Quality. Quality is the prerequisite, and the demand for quality is endless. Total service life and life between regrinds serve as evaluation indicators. ② Price. Price plays a greater role in fully competitive markets, measured by cost-performance ratio. ③ R&D capability. The ability to launch new products includes two aspects. First, responsiveness to customer demands. Users worry that tool suppliers ignore their requirements: suppliers aggressively promote unwanted products while delaying solutions for products the customers actually need. This situation has improved greatly, and targeted mature solutions are now available. Second, the capacity to design and manufacture new products, which tests suppliers’ technical and manufacturing strength.

Not all customer requirements are reasonable or feasible. Nevertheless, suppliers (including ourselves acting as suppliers for others) are obligated to carefully analyze customer demands and deliver professional solutions based on existing technology. The capability to provide professional and targeted technical solutions under current technical conditions is a crucial practical test of a supplier’s R&D capacity.

④ Delivery lead time. Reducing inventory has become a necessity in all fully competitive industries, so shorter delivery lead times are highly important. Establishing reasonable inventory close to customers is a practical solution; proximity enables faster delivery. Cutting tool suppliers are no exception.