Metal Removal Counts

The rate of metal removal is the first of many considerations a machine designer faces when developing new lathe.

Most jobbing shops are looking for this feature. They want high metal removal rates and high accuracy too and you have to combine these features with price. You also have to design a lathe that’s competitive and make it a quality product right up from the base and bed casting to the gears and headstock.

A potential user of an engine lathe or any other machine tool- would look for performance first. He would check out a machine as a car.

Spindle speeds are a major consideration today. Most engine lathes are around 2000 rpm but an equally important consideration is the lathe’s ability to take full horsepower cuts at the lower spindle speeds.

Due to its design, for example, a lathe safe at 5 hp may be able to utilize the full 5 hp at the higher spindle speeds; a good lathe, however, will comfortably take full horse cuts as low as 300 rpm.

In order to efficiently cut a variety of metals of various diameters at optimum surface speeds, the horsepower capability throughout the range of spindle is of prime importance.

Not only should the engine lathe be able to take a full horsepower cut at low rpm, but it should be rigid – there should be no chatter. That’s when the design and quality of the casting are important; a machine, which is not sufficiently rigid, will produce vibration under heavy cutting forces and consequently chatter.

Casting is a scientific process, and there’s no real way a manufacturer can assure a customer that one casting is better than another. The heavy machine is not necessarily the best machine. Although metal casting for machine bases are about three times more expensive to produce compared with welded steel fabrication their superior vibration absorbing qualities over long period continue to make them the preferred choice.

Accuracy, even in small engine lathes, has increased in recent year due to demand from tool-and-die shops. Some machine tool builders offer specifications that are much tighter that any user needs. It’s like buying a car that goes 160 mph when you can only drive in a 60 mph limit area.

Chucks are generally an option on engine lathes. The chuck’s performance is based on its accuracy and ability to grip the workpiece. You can buy a low cost chuck but you’re going to have problems if you want to grip the workpiece accurately and tightly. The chuck will likely have excessive run out, or, under cut will slip.

You won’t defeat your purpose if you buy a cheap chuck and put it on an expensive lathe. The chuck is just as important to your machine’s performance as your machine is.

The length of the bed is important too. It basically depends on what the lathe is being used for. Heavy metal removal means more horsepower and it’s important to get maximum metal off in one cut.

Unit 4 Laser Drilling Technology

Laser drilling is accurate and repeatable. It offers an attractive and essential technique for drilling holes in materials that will be developed in the future.

In fact, laser drilling applications are now emerging in the aerospace and automotive industries, where large volumes of holes are produced o a daily quality production rate.

In particular, the auto industry has been looking into laser applications for some time. At present, one application in the automotive industry is using laser to drill lubrication holes in car transmissions.

The main advantage of lasers for the automotive and aerospace industries is the ability to allow design latitude for drilling, cutting and welding. The flexibility offered by lasers for drilling holes in difficult locations, and for accommodating design changing, provides increased cost effectiveness for producing applications.

For example, one U.S. auto maker currently uses a laser to drill three lubrication holes in an internal gears used in transmissions. Previously the company used carbide bits to drill the holes, but the bits wore out or broke after six or seven holes.

A laser removes material by melting and vaporizing it. The energy density for normal hole drilling is over five million watts per sq. in, and the resulting heat is capable of vaporizing diamond, tungsten carbide, or any high temperature metallic or ceramic material.

A laser can produce holes as small as 0.0002 in dia, while holes larger than 0.050 in are trepanned or cut out. In general, industrial lasers are limited to a maximum of 1 in in-hole depth that can be drilled efficiently.

The major elements of a laser system are a laser cavity, power supply, optics, beam delivery system, support structure, laser enclosure, system control, and exhaust system.

The primary types of laser used in material processing are the Neodymium-dopes Yttrium Aluminium Garnet (YAG) laser and the CO2 gas laser. Other lasers used in material processing to a lesser extent, are excimes gas, argon gas, neodymiumglass, and alexandrite.

The YAG laser is especially suited for drilling and cutting metals. Most metals reflect much of the incident light energy emitted by lasers, but the YAG couples its energy better than most lasers.

For typical drilling operations, certain YAG system can penetrate up to 25 mm thicknesses of material. Hole sizes ranges from 0.1 mm up to a maximum of about 1 mm without beam, manipulation. With beam or part manipulation, almost any size or shape hole can be cut.

CO2 lasers are suited for cutting organic materials and synthetics such as plastics, rubbers, cloth, and paper. They also perform well for cutting, welded, and heat-treating iron and its alloys.

YAG and CO2 lasers can operate either in pulses or in continuous mode, with the pulsed mode usually being most effective. The number of pulses required to drill a specific hole depends on the hole diameter, material thickness, and material properties.