Direct part marks (DPM) make it possible to identify a component throughout manufacturing, assembly and service without relying on a paper label. A Data Matrix code can be laser etched, chemically marked, molded or applied by dot peen directly onto metal or engineering plastic.
Permanent marking improves traceability, but it also creates a demanding reading task. The code may have low contrast, uneven cells, reflections, curved geometry or machining texture. This guide explains how to select and integrate scanning equipment for DPM codes.
What is a direct part mark?
A direct part mark is a machine-readable symbol placed permanently on the surface of a component. Data Matrix is widely used because it can store useful data in a compact area and includes error correction. DPM is common in automotive, aerospace, electronics, medical devices, tools and industrial equipment.
Unlike a printed label, a DPM code is created by changing the surface itself. That difference affects both image contrast and illumination. A normal barcode scanner designed for dark ink on white paper may not read every direct mark reliably.
Common DPM marking methods
Laser marking
Laser systems can change surface color, remove material or create a fine etched pattern. The result can be sharp and compact, but contrast varies with the material, coating and laser parameters. Polished metal may reflect the scanner's light even when the mark looks clear to the eye.
Dot-peen marking
A dot-peen machine creates a pattern of small indentations. The cells are not continuous printed squares; the reader must recognize the geometry from highlights and shadows. Lighting angle is often critical.
Chemical etching
Chemical or electrochemical marking can produce high-quality permanent symbols on conductive materials. Surface preparation and process consistency affect edge definition and contrast.
Molded or cast marks
Plastic and metal parts can include the code in the mold or casting tool. These marks may be raised or recessed and can have the same color as the surrounding material. Part texture, draft angle and wear of the tool can change readability.
Why DPM codes are difficult to scan
DPM reading problems usually come from a combination of factors:
- Low contrast: the symbol and background may have nearly the same color.
- Specular reflection: polished metal creates bright glare that hides cells.
- Uneven cell shape: dot-peen marks may vary in depth, diameter or spacing.
- Surface texture: machining lines, rough molding and coatings add visual noise.
- Curvature: cylindrical parts distort the code and move some cells out of focus.
- Small module size: compact components may require high optical resolution.
- Contamination: oil, dust, oxidation and process residue change the appearance.
A capable DPM reader must capture useful contrast under these conditions and apply decoding algorithms designed for non-printing marks.
1. Start with real marked samples
Do not select a reader from a clean sample image alone. Collect parts from normal production, including the lowest acceptable marking quality, different materials, coatings, colors and surface finishes. Include samples after washing, assembly or any process that may change the mark.
Record the Data Matrix size, number of rows and columns, module dimension, marking method and available reading distance. These details help the supplier select optics and illumination.
2. Match optical resolution to the module size
The smallest cells in the code must occupy enough pixels in the captured image. A reader with a wide field of view may cover several possible part positions but provide insufficient resolution for a tiny symbol.
Define both the required field of view and the smallest module. For handheld use, the operator may move closer, but the scanner still needs a practical working range. For fixed-mount systems, part presentation and lens selection should keep the mark inside the field of view and in focus.
3. Use illumination that reveals the mark
Lighting is often the most important difference between paper-label scanning and DPM scanning. A specialized reader may combine several illumination modes:
- Diffuse light reduces harsh reflection on moderately glossy surfaces.
- Low-angle light creates shadows that reveal dot-peen indentations and embossed cells.
- Polarized light can reduce glare from certain surfaces.
- Direct bright-field light works for marks with strong color or reflectivity differences.
The best mode depends on the part. Test the scanner at realistic angles rather than assuming one illumination setting will work for every component.
4. Control reading angle and distance
A small change in angle can move glare away from the camera and make a metal mark readable. Handheld DPM readers often allow the operator to tilt the scanner naturally. Training should show the practical distance and angle for each part family.
In fixed stations, use a rigid adjustable mount and a fixture that presents the mark consistently. Avoid an angle where the illumination reflects directly back into the lens. If parts vary in height, confirm that depth of field covers the complete range.
5. Plan for curved and irregular surfaces
A code on a cylinder may wrap around the surface, changing cell shape and focus across the symbol. Keep the mark small enough relative to the diameter and position the reader so the code faces the camera as directly as possible.
If the part cannot be oriented consistently, a handheld reader may be easier than a single fixed camera. Automated systems may require multiple views or mechanical rotation.
6. Separate marking quality from reader capability
Powerful decoding can read a marginal mark, but it should not hide an unstable marking process. Monitor laser focus, dot-peen stylus wear, mold condition and part surface preparation. Define an acceptable quality standard and inspect representative samples.
Track which parameters cause failures. Low contrast, missing cells and geometry distortion require different corrective actions. A stable process provides more reading margin across scanners and production locations.
7. Test the complete workflow
A successful laboratory read is only the first step. Test the code after every relevant manufacturing process and in the real workstation. Include ambient light, gloves, fixture access, cycle time and the required host interface.
For a fixed reader, verify trigger timing, result communication and no-read handling. For handheld use, measure first-read rate and scanning time across several operators. If the application records serial numbers, confirm that data is assigned to the correct part.
Handheld vs fixed-mount DPM readers
A handheld DPM scanner provides flexible angle and distance, making it suitable for manual assembly, inspection and service. It can also support many part shapes at one station.
A fixed-mount reader is better for repeatable automated cycles. It requires more control over part position, lighting and triggering, but it can integrate directly with a PLC or production system.
The choice depends on takt time, automation level, number of part variants and available space. Some projects use both: fixed scanning in production and handheld scanning for exceptions or rework.
Frequently asked questions
Can a normal 2D barcode scanner read DPM codes?
It may read high-contrast marks, but performance can be inconsistent on reflective, dot-peen, curved or low-contrast surfaces. A DPM-capable scanner normally provides specialized illumination and decoding.
Which code is most common for DPM?
Data Matrix is widely used because it is compact and supports error correction. The required data format and marking rules depend on the industry and customer specification.
What information should be sent to a scanner supplier?
Send physical marked parts when possible, plus the material, finish, marking method, code size, module dimension, reading distance, angle range, cycle time, ambient light, interface and target first-read rate.
Can oil or dirt prevent DPM reading?
Yes. Contamination can fill indentations, reduce contrast or create reflections. Test parts in the expected condition and define cleaning or process controls where necessary.
Choose equipment around the marked part
DPM success comes from matching optics, illumination, decoding and workstation design to the actual material and mark. Evaluate production samples, control presentation and test the complete workflow before rollout.
Explore Techbarcode industrial scanning solutions or contact our team with sample parts and integration requirements for a DPM evaluation.