High-Precision Multicavity SEM Vacuum Shell Production Case

About Product

SEM (Scanning Electron Microscope) is a precision device used to observe the microstructure of an object’s surface. Unlike an optical microscope, which relies on visible light, an SEM uses an electron beam as its light source. This beam irradiates pooled electrons onto the sample to react. And then the electron receiver accepts and amplifies the signals of secondary electrons and backscattered electrons for imaging.

Electrons in an SEM are generated through thermal dissociation. To prevent the filament from oxidizing at high temperatures, the process must be carried out in a vacuum environment. SEM is widely used in high-end research in new materials, biomedical science, and many other fields due to its high resolution and large magnification range.

Custom Vacuum Shell for SEM

SEMs are highly sophisticated instruments with long service lives and high costs, resulting in low annual demand. As a result, these devices are typically customized, with components manufactured individually based on the customer’s specific needs rather than through mass production.

Our customer, a supplier of laboratory electronic equipment primarily for SEMs, has sold their products to over 400 universities, enterprises, and research institutes worldwide. This time, the customer approached WayKen to produce the vacuum shell in SEM. Let’s check how WayKen handles this project effectively.

Part Structure Analysis and Solutions

This vacuum shell of SEM is a large, heavy, hollow box with grooves and threaded holes arranged in a regular pattern on four sides. All surfaces, except the grooves, should be polished smooth. To balance cost and delivery time, WayKen’s engineers consider choosing a cost-effective machining solution, combining Wire EDM and CNC machining.

In this vacuum shell, all square grooves have a deep cavity and the aluminum Al6061-T651 has a high strength, which requires the machine to have enough cutting strength.

Machining Solutions of Vacuum Shell

First, WayKen utilizes Haas VF series machines with BT40 spindles, which can achieve feed speeds up to 21.2 m/min. These machines are well-suited for milling large parts and removing a lot of material. We choose this type of machine to manufacture the vacuum shell for their strong cutting strength, also shortening the production time.

Next, although wire-cut EDM leaves a rough surface, it was chosen to remove the intermediate material of the vacuum shell due to its high efficiency in cutting deep cavity structures. However, to meet the roughness requirement and short lead time, we left a 1 mm margin during wire EDM. And then uses CNC machines to sweep away the rough traces. In this way, the polishing time and cost would be saved a lot.

Key Machining Focus: Dovetails and Their Solutions

To ensure the vacuum shell’s airtightness, the customer designed grooves of two different shapes. As shown in the picture, the outer groove is a dovetail, known for its high internal stress and strong anti-leakage properties, making it ideal for vacuum sealing. This dovetail groove will be fitted with a spiral shield, serving as the primary defense against external air. Inside, there’s a standard rectangular groove that will hold an O-ring, acting as a secondary sealing structure.
In order to achieve the sealing function, the size of the sealing groove is particularly critical. Under certain pressure, the grooves must allow space for the O-ring and spiral shield to expand without being so wide that they risk falling out. Therefore, the grooves must be milled with extreme precision, maintaining a tolerance of ±0.005 mm.

How to Achieve Machining Dovetail？

In this vacuum shell part, we need to focus on the machining of the dovetail groove, as shown in the picture below. WayKen customized a dovetail cutter, whose diameter is smaller than the width of the groove and has a blade fitting the beveled edge of the groove, to manufacture this shaped undercut.

The machining process begins with roughing, where the cutter removes most of the material, leaving a margin for finishing. Next, the cutter is used for finish machining at a slow speed, gradually milling the groove’s structure. This process ensures the groove is machined precisely, with the tolerance controlled within ±0.005 mm. At the same time, as the cutting volume of every milling is small, the surface finish can achieve Ra 3.2μm.

Strict Inspection to Ensure Assembly

The vacuum shell features numerous screw holes on all four walls, which are critical for ensuring a tight assembly with other components. These holes must meet a tolerance of ±0.005 mm. WayKen used Zeiss CMM to measure the hole distance. It can determine the position of circles through probes taking points around the hole. And the software can help accurately locate the center of the circle, measuring the hole distance accurately. After inspection, all tolerances including hole distance were met.

Feedback and Plan

After receiving the vacuum shell, it was immediately installed on the SEM’s vacuum system, and it is operating perfectly. “It’s incredible that WayKen could produce these vacuum shells with such complex processing flow, perfect sealing function, and high precision requirements within two weeks.”The customers are impressed with our exceptional production capabilities and efficient management.

With comprehensive machining capabilities, WayKen delivers high-quality custom components with tight tolerances and complex structures. Combine advanced manufacturing techniques and efficient project management, we consistently meets product demands for precision, cost, and quick turnaround times. Just contact us today, let’s start your project!