High-speed machining centers are used in the production of automotive parts.

The automotive industry, compared to machining industries such as aviation, aerospace, shipbuilding, and machine tools, is characterized by its large production volumes and short processing cycles. To accommodate the mass production of single workpieces, the use of specialized machines or automated lines of specialized machines is the most economical and thus the most common choice. However, the current demand from automotive users for diversified and personalized vehicles is forcing automotive companies to change their product models more rapidly, resulting in a wide variety of products. The original mass production of single workpieces has transformed into mass production through the iteration of smaller batches of multiple workpieces. Therefore, the traditional modular machine tool (specialized machine) production lines that have dominated the automotive manufacturing industry for many years can no longer meet the rapid updates required by the industry. Although specialized machines or automated lines of specialized machines are efficient, they limit processing flexibility, making the machines poorly adaptable to changes in the types of parts processed.

To address this challenge, a new generation of high-speed, high-efficiency machining centers—high-speed machining centers—has emerged. They effectively resolve the conflicts between processing flexibility and production volume, investment, and updates, meeting the current requirements of the automotive industry for diverse products, large volumes, and low investment. They also satisfy these requirements for the production of automotive components.

Characteristics of High-Speed Machining Centers

A high-speed machining center refers to a type of machining center with a spindle speed exceeding 10,000 r/min, a feed rate exceeding 40 m/min, and a feed acceleration greater than 0.5G (5 m/s²). To achieve stable processing at high speeds and large cutting volumes, high-speed machining centers typically have the following structural characteristics:

1. High-Speed Spindle

A spindle speed that is too low cannot meet production efficiency requirements, while a speed that is too high introduces various不利 factors in terms of reliability. The spindle speed of high-speed machining centers is usually set between 46 and 16,000 rpm. For this purpose, the optimal structural solution is an internally mounted direct-drive electric spindle, which is non-detachable, requires no maintenance, and needs no adjustment. The spindle rotor is mounted on composite ceramic ball bearings and supported at three points to ensure high dynamic rigidity and precision. There is a dedicated water cooling system around the stator and rotor bearings to absorb heat.

1. Structural Design for Dynamic and Thermal Balance

Due to their high spindle speeds, high feed rates, and high feed accelerations, high-speed machining centers necessarily require a structural design with high static and dynamic rigidity. To this end, some separate the hydraulic devices from the spindle to reduce the impact of vibration on spindle accuracy.

The equipment structure is completely thermally symmetrical to avoid positional shifts between the spindle and the workpiece due to thermal deformation. To prevent chip heat imbalance, which is a significant heat source, some designs ensure that chips do not remain on the workpiece or pallet. Instead, they quickly discharge the chips to the cutting fluid tank through spiral chip conveyors on both sides of the Z-axis cover, minimizing the thermal impact of the chips.

To ensure motion rigidity and stability, the design of high-speed machining centers typically follows these principles:

(1) The forces applied to each axis are always along the axis of each center of gravity to avoid swinging of structural components during acceleration and deceleration.

(2) The guiding devices for moving parts are also located on the plane of the center of gravity to stabilize the equipment structure and avoid swinging of structural components during acceleration and deceleration.

(3) A component inlay structure is adopted, and the processing technology of components is improved to reduce the weight of moving parts.

(4) Measurements for each axis are taken at the thrust center to obtain the most precise measurement results and the greatest stability in positional repeatability.

1. High-Rigidity Three-Point Supported Bed

High-speed machining centers mostly use a three-point supported bed similar to coordinate boring machines. Through finite element analysis (FEM), a high-rigidity structural design is achieved, maintaining high rigidity and stability for optimal rigidity during processing at maximum travel speeds, even when heavy cutting and multiple positioning movements are required.

1. Linear Rolling Guides Combining Rigidity and Precision

The maximum feed rate and rapid traverse rate for each axis of high-speed machining centers are generally above 40 m/min, all achieved through precise, anti-friction linear motion ball screw guide systems. The ball screws use preload ball bearings with no backlash, and the guides are lubricated with a quantitative lubrication system supplied by a central lubrication unit. This system offers excellent stability and dynamic rigidity, enabling rapid response to computer commands. Some machines use a new type of structure for the ball screws in all three axes. To minimize rolling inertia, the screw is fixed and does not rotate; instead, a digital motor drives the ball screw nut through a toothed belt.

1. Adoption of HSK Clamp-Type Tooling

The HSK clamp-type tooling clamping method is specifically designed for high-speed machining center tools. It has strong static and dynamic rigidity and can transmit torque safely and efficiently.

1. Rapid Tool Changing and Pallet Exchange

In a machining cycle of a machining center, tool changing time and pallet exchange time often account for a significant portion. On traditional non-high-speed machining centers, tool changing time (chip-to-chip) is around 14-20 seconds, while pallet exchange time can take 3 minutes or even longer, which is clearly unsuitable for the high-volume, fast-paced production requirements of automotive parts processing. High-speed machining centers, on the other hand, are designed to match their high spindle speeds, high feed rates, and feed accelerations in these two aspects, with tool changing time (chip-to-chip) reaching approximately 3.5 seconds and pallet exchange time reduced to just 6 seconds. Each pallet is equipped with a precision ratchet indexing mechanism to ensure accurate 360° indexing. If required by the user, 360,000 indexing positions can be provided, offering high flexibility for processing various surface parts and rigidity during operation.

Application of High-Speed Machining Centers in the Automotive Components Processing Industry

1. Application in the Automotive Components Processing Industry

Currently, various large, medium, and small high-speed machining centers, with single or dual spindles, ranging from manual loading/unloading single-pallet types to multi-pallet flexible manufacturing units, have been widely applied in the automotive components industry. They are primarily used in production lines for cylinder blocks, cylinder heads, differential cases, connecting rods, gearbox cases, steering knuckles, and various other parts, demonstrating excellent overall performance.

Depending on production volume and user demand, high-speed machining center production lines can be arranged in series (process-dispersed), parallel (process-concentrated), or hybrid configurations. Currently, hybrid configurations are the most widely used in automotive industry production lines, offering optimal production efficiency, sufficient flexibility and reliability, and facilitating production line layout for phased batch production. The number of parallel machines in a hybrid configuration should be between 1 and 4.

In the early 1990s, there was an excessive emphasis on the requirement for high processing flexibility, overlooking the limitations of high-speed machining centers in certain processing technologies. After years of exploration, it is now believed that a reasonable automotive parts production line should adopt a combination of dedicated and flexible solutions. For example, for the processing of automotive engine cylinder heads and blocks, the dedicated-flexible combination solution can be summarized as follows:

(1) Planar processing: Aluminum parts – high-speed machining centers; cast iron and steel parts – CNC milling machines.

(2) Medium and small holes, threaded holes – high-speed machining centers; irregular and small planar milling – high-speed machining centers.

(3) Important special surface processing (boring cylinder holes, crankshaft holes, camshaft holes, long oil holes) – flexible specialized machines or modular machine tools.

Production lines primarily composed of high-speed machining centers have the following characteristics:

(1) They can easily be implemented in stages according to production volume requirements and investment availability, allowing for gradual expansion of equipment.

(2) Large-scale adjustments and equipment updates are not required when changing product types. A production line built with a one-time investment can not only meet current market demands but also future demands for new product production.

(3) Due to their high cutting speeds, high feed rates, and short auxiliary times for tool changes, they offer high production efficiency.

Since most of the equipment on the production line consists of the same model, it is easy to master, maintain, and prepare spare parts, ensuring a high equipment availability rate.

Conclusion

With the rapid development of China's automotive industry and the current volatile automotive market, each automobile manufacturer can only maintain a proactive and advantageous position in the market by producing high-quality, low-cost, and diversified automotive products. The emergence and development of high-speed machining center processing technologies and methods provide an economically feasible and efficient solution for the development of China's automotive industry, especially the automotive components sector. Dual-spindle machining center