Making your mark

Oct. 1, 1999
When it comes to identifying a part, companies can choose among mechanical, electrochemical, and laser marking technologies.

When it comes to identifying a part, companies can choose among mechanical, electrochemical, and laser marking technologies.

The Eternagraphix process, created by George Industries, Los Angeles, produces full-color, photographic-quality graphics in anodized aluminum and powder-coated finishes. Graphics, from high resolution illustrations and camouflage patterns to richly detailed photographs, can be a part of the surface of a product. The Eternagraphix finishes are said to be as durable as the anodize, hard anodize, or powder-coated finishes in which they are integrated.

A "Floating-pin" technique lets a marking pin accommodate surface irregularities.

The Pannier MSG 3000 Programmable Stamping System is designed to permanently mark large parts on an assembly line.

The LaserMate laser engraving systems from Online Inc., McHenry, Ill., can permanently mark anodized aluminum surfaces at over 100 characters/sec.

A beam-steered laser marker has a high-speed, computer-controlled galvanometer controlling each axis of beam motion.

Typically, shops use marking technologies to identify their products, although some may use them for cosmetic purposes. Whatever the reason, the demand for faster speeds and better quality marking methods has fostered the development of a number of innovations. Many current marking techniques are the result of incremental enhancements to traditional technologies, while others represent creative, radically different approaches.

Wham, bang goes high tech
The granddaddy of all product-marking techniques is the venerable steel handstamp. With each swing of the hammer, parts are marked with one or more characters. Although it is a low-production, low-budget method of marking, with limitations in character size, the amount of information that can be marked, and marking uniformity, handstamping is still common in most manufacturing shops.

Although still based on marking by indenting a part, the technology has evolved in several different directions each offering specific capabilities.

Hand-held air impact markers are commonly used for instantaneously indenting a permanent mark into various metal and non-metallic surfaces—such as wood. These markers range in price from $150 to $2,000. They are rugged with few mechanical parts and are self-contained for ease of use and reduced maintenance.

Replacing all wearable components on standard air impact markers (not including tooling) is usually less than $60 and often takes less than an hour. Regular toolroom personnel can perform the maintenance.

An example of a versatile air impact marker featuring a quick-change stamp holder is Columbia Marking Tools' new Model 95, a heavy-duty, single-blow, portable air impact marker for permanently marking parts with operator codes; inspection, date or assembly data; or quality-control or job-station information. According to the Mount Clemens, Mich., based company, the Model 95 marks forgings and castings and can be used for small assembly staking and pindriving operations.

The simplest air impact markers are single-acting types that use pneumatic power to strike the workpiece at forces ranging from approximately one to eight tons, depending on supplied air pressure. The more costly of these products feature shock-absorbing bumpers at both ends of the stroke to prevent damage to the marker when fully extended on the forward stroke and to reduce shock on the return stroke.

Double-acting air impact markers propel the rod both toward and away from the workpiece. The air return feature allows use of a sensor or limit switch on the return stroke to indicated the marker is retracted.

Typically, these portable systems have an airactuated rod housed within a cylinder that is capable of containing and efficiently venting compressed air, a stamp holder (usually integral with the rod), and stamps. A system of air valve and the operator— or automatic cycling devices—control the impact of the stamp end of the rod into the workpiece.

The stamps, made of hardened tool steel, are durable and easily replaced. Stamp life of an air marker is a function of the number of parts marked, cycle time, material, number of characters marked, and the force of the marker. It is not unusual to mark 100,000 parts before stamp replacement is necessary.

Roll marking machines are designed to mark round, flat, and irregular shaped parts quickly and quietly. Roll marking produces uniform impressions and uses low marking pressures compared with press applications.

Columbia Marking Tools' new Model 2640 barstock rolling machine simultaneously imprints continuous identification information on hexagonal barstock, eliminating the need for secondary marking operations. Fitting sizes, types, lot numbers, part numbers, company logos or trademarks, and even date codes can be roll marked on three or four sides of hexagonal stock. The Model 2640 can also mark square and round barstock, particularly beneficial to fitting manufacturers that typically have wide variations in part sizes and types. Brass, stainless steel, alloy and cold-rolled steel barstock can be marked equally well in sizes from 3 /8 to 2 1 /2 in.

Dot peen marking is a versatile technology based on making indents with a vibrating stylus. The method provides neat, clear, and permanent marking of characters, digits, barcodes, and logos on metals, plastics, glass, wood, and other rigid materials. The vibrating stylus does not weaken the material being marked, regardless of its thickness.

An example of this marking technique is the Pro-Pen P3000 dot peen marking system from Marking Methods Inc., Alhambra, Calif. The machine marks one to five characters/sec, depending on character size and tool used. The P3000 is compact and weighs only 64 lb, so one man can easily install it on a workbench or transport it to multiple locations. Prices start at $6,500.

Pneumatic "floating pin" indenting, patented by Telesis, Circleville, Ohio, and the basis of the company's Pinstamp System, features a pneumatically-driven and returned conical tipped pin that permanently indents a marking surface to form either dot matrix or continuous-line characters. Since the pin "floats" on constant return air pressure, surface irregularities up to 1 / 4 in. can be accommodated.

The floatingpin approach eliminates the need for a pin return spring—a high maintenance component required by other pin markers. Marking impact can be controlled by varying the pin stroke, air pressure adjustment, or by selecting pins of different sizes and weights. The system marks materials with a wide range of hardnesses from soft plastics to hardened steel.

Programmable marking systems, such as the MSG Programmable Stamping System from Pannier Corp., Pittsburgh, is controlled by stamping information downloaded to the mark-ing-head controller from a host computer, PC, PLC, or read with a bar-code wand. The barcode reader converts barcode information from the printed page to an RS-232 signal that is recognized by the controller.

The marking unit uses a pneumatically driven stylus to stamp or emboss a series of very small, closely spaced marks forming straight or curved lines. The carbide stylus tip oscillates hundreds of times per second to perform micro impacts on the surface of the material to be marked.

A portable system, specially designed for marking large parts, is held in place with electromagnetic clamps and eliminates the need for marking products with hand stamps, ink jets, or attached tags.

Stress-free metal marking
Electrochemical processes permanently mark almost any image without stress to even thin-walled metal parts. A system from Marking Methods can create permanent marks from 0.0001-in. deep for parts such as feeler gages to over 0.010-in. deep for products such as aerospace components requiring traceability for life of the part. Character sizes can be as small as 0.030 in. to over 2.0 in. and can be marked into any conductive metal including aluminum, brass, carbide, nickel plate, stainless steel, titanium, and heat-treated metals. The process involves placing the part to be marked on a ground plate and positioning a stencil, then placing a marking applicator, moistened with electrolyte, on top of the stencil for a second or two. The marked part is then wiped with a cleaner.

A power unit produces a safe electrical current that uses the electrolyte (a mild pH-balanced, buffered salt solution) to pass through the stencil to mark the exposed metal area. The resulting mark is permanent and can only be affected by buffing or grinding down to the depth of the mark.

Marking with light
Laser marking is a thermal process that employs a high-intensity beam of focused laser light to create a contrasting mark. The laser beam increases the surface temperature to induce either a color change in the material and/or dis place material by vaporization to en-grave the surface.

A beaming steered laser marker provides the greatest degree of image manipulation.

To create the marking image, two beam steering mirrors mounted on high-speed, computer-controlled galvanometers direct the laser beam across the target surface. Each galvanometer provides one axis of beam motion in the marking field. The beam projects through a multi-element, flat-field lens assembly after reflecting off the final steering mirror. The lens assembly focuses the laser light to get the highest power density possible on the work surface while maintaining the focused spot travel on a flat plane.

The combination of a Nd:YAG (Neodymiun: Yttrium Aluminum Garnet) laser and the beam-steered delivery system provides the widest range of materials and offers the versatility of computer-controlled image generation. Beam-steered Nd:YAG provides more marking power and far superior imaging than any other laser marker configuration. The available high peak power can mark or engrave a wide variety of materials including hardened metals. Beam-steered Nd:YAG mark-ers frequently replace marking systems that permanently mark products by imprinting or engraving. For example, the Insignia Nd:YAG marking system from Control Laser Corp., Orlando, is compatible with a wide range of metallic, synthetic, and organic materials. The system has the power and performance to permanently apply intricate graphic images from within advanced, automated manufacturing lines.

A continuous-wave CO2 laser can also be combined with the beam-steered delivery system. However, the lower power CO2 marker does not provide the power to engrave substrates but, due to its comparative simplicity, is significantly less expensive than a beam-steered Nd:YAG marker. Beam-steered CO2 systems are frequently used for marking general plastics and plastic and ceramic connectors and electronic packages.

Reading the bumps
Bumpy Bar Codes are 3D barcodes that are directly stamped, embossed, or molded into metal, rubber, or plastic products. Represented by highs and lows in surface height, rather than changes in black and white as in traditional barcodes, they can survive in harsh environments that would render traditional black and white barcodes useless.

The Bumpy Bar Code 1410 Reader, produced by Sensis Corp., DeWitt, N.Y., reads and decodes 3D barcodes. The reader works by illuminating the barcode target with a laser and capturing the reflected image in a 2D CCD (the same technology used to capture images in a video camera). The angular displacement between the laser and CCD array provide the basis for the detection of the differences in height across the Bumpy Bar Code.

By manufacturing the shallow barcode into a product, a permanent 3D barcode is embedded that lasts for the life of the product.