Workshop Techniques: Maintaining Dimensional Stability in Sheet Machining
In precision thin plate machining, have you ever been troubled by part deformation and difficulty in controlling precision?
Machining thin plate parts presents a significant challenge, especially in fields like aerospace and electronics, where maintaining dimensional stability and surface integrity under cutting and clamping forces is crucial. This article reviews a comprehensive set of process solutions based on various real-world machining cases, covering everything from simple thin plates to complex structural components and ultra-thin foils. By implementing practical methods such as optimizing clamping designs, adjusting machining strategies, and introducing flexible supports, we have successfully minimized machining deformation. This approach has led to significant improvements in both quality and efficiency.
Whether you are a process engineer or a front-line operator, I believe that reading these practical experiences from the production site will inspire you.
1 Introduction
The widespread use of precision thin plate parts in industries such as aviation, aerospace, satellites, electronics, and nuclear power highlights the importance of high-efficiency and high-precision machining. Controlling machining and clamping deformation has consistently posed challenges in the production of precision thin plate parts. This article presents machining solutions for simple, complex, and ultra-thin plate components, utilizing actual case studies, to ensure that product precision requirements are met.
2. Machining of Simple Thin-Sheet Parts
Simple thin-sheet parts are typically small in size and have uncomplicated shapes. Due to their small dimensions, they cannot be cut into individual pieces, as they are unsuitable for clamping with standard fixtures like vises. Generally, all six sides of these parts need to be machined with precision. Using multiple clamping operations can easily lead to errors, which compromises both machining efficiency and quality.
Through research and exploration, the following machining method has been developed:
1) Start by cutting a single large sheet to machine multiple parts simultaneously. A fixture plate is created (see Figure 1). The sheet material is then securely clamped onto the fixture plate using pressure plates, allowing for the precision milling of both end faces.
2) An adjustable-length clamping plate is used to secure machined parts, preventing the workpiece from becoming detached from the main board and avoiding tool collisions at the end of the milling process. The machining toolpath for the finish milling of the workpiece shape is illustrated in Figure 2.
3. Machining of Complex Thin-Sheet Parts
Complex thin-sheet parts often require machining due to their numerous features, which typically include hole systems, grooves, and steps. During the machining process, auxiliary holes can be effectively created using through holes or grooves. To clamp and position the part, screws, washers, and bosses are utilized on the fixture. Adjusting the clamping position ensures that all machined areas are completely processed while maintaining a consistent clamping state throughout the operation. The machining scheme for a specific complex thin-sheet part is as follows:
1) Design and fabricate a fixture plate according to the final machined shape of the workpiece (see Figure 3). Pre-drill locking screw holes and pressure plate screw holes on the fixture plate.
2) The initial step in part machining is to secure the workpiece using a pressure plate against the fixture plate, ensuring rough alignment. Pre-machine the holes in the workpiece. (leaving machining allowance for the hole dimensions).
3) The second step in part processing is clamping, as shown in Figure 5. To secure the workpiece, install four screws around the perimeter and one screw in the center. After that, remove the two side pressure plates and mill the upper end face, holes, grooves, and outer contour of the workpiece.
4) The clamping setup for the third step of part processing is illustrated in Figure 6. First, remove the original screws and install six new screws on the inside. Utilize the two pressure plates at both ends to assist with clamping. Mill the interference area on the upper surface, then proceed to mill the four holes around the perimeter, as well as the large hole in the center, to complete the processing.
This solution addresses the challenge of clamping complex thin-plate workpieces. For thin-plate parts with a thickness of 3-5 mm, it allows for the simultaneous processing of multiple pieces, ensuring product quality while significantly enhancing processing efficiency.
4. Processing of Ultra-Thin Plate Parts
When it comes to ultra-thin plate parts, which typically have a thickness of 0.05-0.15 mm and are made from materials like stainless steel and non-ferrous metals, they are often used as washers or shims. Due to their thinness, traditional mechanical clamping methods are not suitable. To accommodate their structural characteristics, raw materials are purchased in sheets of the same thickness as the final parts. These sheets are manually cut to the required dimensions and secured using upper and lower pressure plates and screws arranged in multiple layers, or they may be fixed using welding under pressure.
Subsequently, a fitter drills wire holes, and the CNC spare parts are processed using an Electrical Discharge Machining (EDM) machine. The inner holes are precisely cut through the wire holes, followed by the precise cutting of the outer shape from the outside. The specific process is as follows:
1) The upper and lower pressure plates press the cut sheet material together (see Figure 7), and then secure it using welding or screws.
2) Electrical discharge machining (EDM) is carried out using a wire EDM machine. Initially, the wire is passed through the central wire hole to accurately cut the inner hole of the part. Next, the wire is threaded from the outside to precisely shape the outer contour of the part. The results of the wire cutting for both the inner hole and the outer contour are illustrated in Figure 8.
Through the above operations, precision machining of ultra-thin sheet metal parts can be achieved. Figure 9 shows the finished product, with a thickness of 0.1 mm.
5. Conclusion
The thin-plate components discussed in this paper are too delicate to be handled using traditional mechanical clamping methods. Consequently, we have summarized several efficient and practical processing solutions that have been repeatedly validated through actual processing experiences. By implementing suitable clamping methods and processing techniques, we have effectively addressed the challenges posed by ultra-thin plate parts as well as the clamping deformation issues associated with complex thin-plate components. This approach has ensured the quality of the processed thin plates and enhanced production efficiency.
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