Lapping 101
Lapping is a free (loose) abrasive machining process in which abrasive particles are suspended in oil or water based slurry. The mixture is fed across the surface of a flat, horizontal rotating plate. This method of processing is an exceptionally precise, low pressure, low heat, burr free grinding process capable of holding extremely tight flatness, parallel, surface finish and thickness tolerances.
Lapping machines range in size (lapping plate diameter) from as small as eight inches to as large as 120 or more inches in diameter. In general there are two basic types of lapping machines and they both operate on the same basic principles.
- Single side lapping machines lap one side of a part. The parts being lapped are held against the surface of the lapping plate by their own weight or by a pressure plate with hand weights or pneumatic down pressure. This process allows us to process parts up to 40 inches in diameter.
- Double side lapping machines are capable of lapping both sides of a part simultaneously. The parts being processed are placed in work holders (carriers) that mesh with inner and outer ring gears to provide a random planetary motion. The double side process is best used in applications that require both sides of a part to be lapped to achieve very tight parallelism, flatness and thickness specifications. The double side process is also capable of lapping parts to thickness as thin as .002 (.051mm)
LAPPING MISCONCEPTIONS, QUESTIONS AND ANSWERS:
Lapping can only remove small amounts of material and is basically a finishing process.
- While the above statement is partially true, however, lapping is capable of a lot more. The lapping process is capable of economically removing as much as .050 (1.27mm) on softer materials. Typical removal is in the .002 - .010 range. Lapping can often replace fly cutting and some grinding process in the first surfacing of castings, and other odd shaped parts. With the processes low heat and burr free material removal and the ability to run numerous parts in one set up, lapping can be a very fast and economical way to prepare your parts for machining.
Certain materials cannot be lapped
- Every material from the hardest to the softest, from ferrous to non-ferrous can be lapped. Hardened tool steels to aluminum to ceramics to plastics and even rubber!
How flat can a part be lapped to?
- Depending on the size and shape of the work piece, lapping can typically achieve flatness readings of .000012 (one light band). Most mechanical seals require flatness readings of .000012 - .000036 (1-3 light bands)
How parallel can a part be lapped to?
- Once again, depending on the part size and configuration, typical parallel capabilities of lapping can be found in the .000050 - .0001 range. Closer tolerances can be achieved with additional handling and processing steps.
How good of a surface finish can lapping achieve?
- There are a few answers to this question. To begin with, parts coming off of a typical lapping operation will usually have a gray matte finish or “charge” of abrasive imbedded into the surface of the parts. This surface condition is usually in the 16 – 32 Ra range. With a subsequent light polishing operation that will quickly become a 6-8 Ra surface finish. With an additional polishing step, surface finishes can reach well below a 1 Ra finish.
What types of parts are lapped?
There are so many applications where lapping is used, the list below will represent just some typical applications:
- Mechanical seals
- Bearings
- Silicon Wafers
- Spacers
- Automotive
- Electronic components
- Heat Sinks
- Disk Drive components
- Saw Blades
- Knives
- Die Castings
- Machined parts
- Hard Anodized parts
- Gauge Blocks
- Jewelry
- Valves
- Washers
- Watch Crystals
- Pump components
- Piston Rings
- Aerospace & Space flight components
- Gears
- Thin Brittle parts
- Injection molded plastics
- Machined Plastics components
- Glass
