Spherical Lapping & Ball Polishing
The existing methods for polishing spherical balls and cups may compromise their roundness. Machines currently employed for this purpose exhibit a failure rate ranging from 10% to 20%. However, Kemet International has devised a machine and process that yields a flawless mirror polish, preserves geometry, and rectifies these shortcomings, all while preserving roundness down to 2 microns. This efficient process is completed in under 9 minutes and is applicable to a wide array of materials, including ceramics, natural metals, and metal alloys.
Applications include:
- Prosthetic Devices such as Hip joints and Cups
- Bearing Manufacture
- Spherical Plain Bearings
- Industrial Rod Ends
- Valve assemblies
- Pump Components
Material that can be polished include:
- Cobalt Chrome
- Stellite
- Ceramic
- Steel
- Other materials may be possible
In 2004, Kemet unveiled their inaugural spherical lapping and polishing machine, primarily targeting the medical sector. During this period, the top hip replacement systems required balls and cups with a roundness and sphericity of <0.002mm. The primary challenge lay not in machining spheres to meet these standards, but rather in achieving a flawless, blemish-free mirror polish while upholding such stringent tolerances.
This pioneering effort resulted in the Kemet SPM, a dual-station lapping and polishing machine. It could function autonomously or complement an existing machining center incapable of attaining the scratch-free mirror polish demanded by the industry. The SPM accommodates spheres ranging from 20mmø to approximately 60mmø, serving both balls and cups. Its two-stage process, employing a special polishing pad and Kemet's ISO 9001:2015 certified diamond compound, requires approximately 7 minutes per stage, delivering a flawless mirror polish devoid of imperfections.
Following the SPM's triumph, Kemet received a surge in spherical applications. However, many of these requests aimed to replace manual hand matching of spherical forms. It became evident that the SPM wasn't the ideal solution, particularly because most of these new aerospace applications didn't necessitate polishing. To address this emerging need, Kemet introduced the KemiSphere, initially a benchtop single station machine, and later upgraded to the KemiSphere II, a PLC-controlled benchtop machine with optional pressure system and fully programmable HMI.
KemiSphere II - Spherical Polishing Machine
The KemiSphere II is a compact single station spherical lapping and polishing machine, perfect for aligning two spherical forms or, with appropriate tooling, achieving roundness better than 5μm with a mirror finish. It seamlessly replaces manual lapping tasks and its benchtop design makes it a valuable asset for any workshop involved in spherical lapping.
These machines offer a highly cost-effective and reproducible method for processing spherical forms into a wide range of surface finishes. They can handle various materials, either individually lapped or matched together. Documenting or validating a manual process can be challenging, which is where the KemiSphere II excels. The HMI enables the storage of component-specific programs, including drive speeds, sweep angles, process times, and pressures. Kemet also provides testing services in their labs, generating test data and samples to address all inquiries before machine acquisition. This ensures that machines are delivered pre-programmed and ready for immediate use, regardless of the application.
- 3 motors with independent variable speed control
- Siemens PLC and HMI
- Pressure application system
- Benchtop machine
- Process parts up to 100mm diameter
- Programmable sweep start and finish point
- Single button process start
- Manual and jog facility for simple machine setting
- CE marked
- Fully guarded with interlocks
- Dimensions: 906 x 1055 x 549mm
- 230V-single phase-50Hz
- Product code: 359316
Polishing Pads for the KemiSphere
The Sphericloth Polishing Squares feature innovative flock length technology, which facilitates a significantly higher polish flow onto the pad surface during the polishing process. This increased polish distribution, coupled with the advanced polishing capabilities of the new flock design, results in a remarkably polished surface.
| Type | Description | 127 x 127mm |
|---|---|---|
| Sphericloth-A | For general purpose, single use spherical polishing pads. | 341998 |
| Sphericloth-B | 341966 | |
| NLH | For high gloss spherical polishing | 341276 |
Spherical Lapping Machine - Floor Standing
The Kemet Spherical Lapping Machine is designed to lap and polish pre-machined spherical balls and cups to a flawless mirror finish, capable of achieving roundness better than 3 microns. It boasts an array of features and benefits, including six motors with independent variable speed for precise control, compact dimensions of 1600 (W) x 820 (D) x 2500 (H) mm, pneumatic application of lapping and polishing pressures, rapid processing with an average time of less than 5 minutes, easy transition from ball to cup polishing, manual and jog facilities for setup convenience, full guarding with auto lifting door access, initial tooling set included, comprehensive manual and training, low operating costs, dual process timers, single-button start, integrated lighting, smooth and quiet operation, and CE marking. It operates on either a 230V-single phase-50Hz or 110V-single phase-60Hz electrical supply, with a maximum air pressure of 3 bar.
Advantages of the machine include its ability to process common materials like Stellite, Ceramic, and Cobalt Chrome, simple fixture designs accommodating various product styles, critical parts made from stainless steel for durability, modular design facilitating easy configuration of manufacturing cells (e.g., multiple polishing or lapping stations), dedicated approved consumable formulations ensuring consistent repeatability, and a built-in cleaning option between stages for enhanced efficiency. The product code is 360061.
Choosing a Kemet Spherical Polishing system offers a range of compelling reasons. Firstly, it's built on proven and established technology, ensuring reliable performance. Say goodbye to laborious hand buffing, as these machines streamline the process with efficiency and precision. Moreover, they possess the capability to rectify failures resulting from other spherical polishing machines, providing assurance of consistent quality. With Kemet systems, you can expect a superior mirror polish that meets the highest standards. These machines excel in holding geometry and achieving roundness better than 2 Microns, delivering exceptional results every time. Additionally, they are versatile, capable of processing common materials such as Stellite, Ceramic, and Cobalt Chrome, further enhancing their utility and value.
Ball Polishing Case Studies
Test Requirements: To polish modular heads
Component/Material: Ground heads
| Process Breakdown | |||
|---|---|---|---|
| Stage | Plate/cloth type | Abrasive type/grade | Process time |
| 1 | Cast Iron | 9 micron SiC/W3 slurry | 8 minutes |
| 2 | NLH cloth | 1 micron diamond compound | 4 minutes |
All ground components were lapped within the standard 8-minute cycle and polished in just 4 minutes using the Kemet Spherical Polishing Machine. This machine proves to be an optimal choice for engineering workshops prioritizing polishing and achieving superior surface finishes across a variety of components.
Test Requirements: To lap 2” Flow Control Ball Valve ready for Chrome Coating (Ra better than 0.4 µm). Roundness better than 10 µm
Component/Material: 2” Non plated Semi Spheres.
| Process Breakdown | |||
|---|---|---|---|
| Stage | Matching | Abrasive type/grade | Process time |
| 1 | Rotary control valve | Silicon carbide 22 micron | 20-35 Minutes |
Components underwent lapping on the Kemet Spherical Lapping Machine and were subjected to inspection every 10 minutes using a roundness machine until achieving a roundness measurement superior to 10 µm. (The parts were initially turned to 40 µm before lapping.)
