Introduction
For years, the use of laser technology has been growing in all industrial sectors. At the request of numerous actors in the rubber and polymer injection industry, REP has worked with laser-specialized partner Laselec and developed a laser technology machine called MLC500 dedicated to the cleaning of industrial parts and injection and compression molds.
What has been done in the past to clean molds?
The following orientations have been followed over the years and brought improvements:
Ultrasonic bath:
This is the most widely used method in several sectors to clean equipment. The process strips off undesired material in a non-aggressive manner. However, it is very costly and polluting. It requires the use of chemical additives (anti-grease agents, concentrated detergents, anti-corrosives, deoxidizers, etc.) This method presents risks to the health of the worker and for the environment. This also makes ultrasonic cleaning quite expensive.
The use of ultrasonic cleaning also negatively impacts the user’s production, because the process is time-consuming, requiring several steps: 1) creation of a high-frequency wave, 2) fluctuations between high pressure and low pressure, 3) appearance of miniscule bubbles during the low pressure periods, known as cavitation, and 4) implosion of these bubbles upon contact with submerged surfaces during high pressure periods. Additionally, some molds must be disassembled to allow them to be cleaned. Moreover, this process can only be used on cooled molds. The production will only restart after the mold has been cooled, cleaned, and reheated once more. At the end of cleaning, it is also necessary to plan time for the mold to dry.
Cleaning by projection:
Several different materials can be projected onto an injection mold in order to clean it: sandblasting, plastic balls, dry ice,… This process needs a low initial cost, but it requires costly consumables that are difficult to store. This technology is slow and, just as with ultrasonic cleaning, it only works with cooled molds. This equipment is operated manually, which results in high labor cost. The latest evolution of the projection technique is the use of dry ice which is not abrasive. Nevertheless, prolonged use of dry ice results in heavy humidity which can lead to the oxidation of molds. This process is also very noisy (over 105 decibels), and therefore requires the use of hearing protection equipment.
Portable laser cleaning:
Theoretically it’s easy to be used on site as the equipment is portable. But it requires important individual protections and a protection of the zone to be cleaned. There is also an important risk for the operator and all other people close to the cleaning area. This equipment is operated manually which results in higher labor costs. The use of a portable laser doesn’t allow for a regular scanning or the cleaning area (variable distance between laser and contact surface, longer paths in some areas,
omission of some areas,…).
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Laser beam impact |
Principle of laser cleaning
Laser cleaning is a non-destructive method, that is to say that only impacts the pollutant and does not degrade the substrate. Indeed, when the beam strikes the material to be cleaned, it creates a highly compressed plasma, which relaxes by creating a shock wave. This sudden expansion volume ejects the dirt. The fast pulse (10ns) prevents thermal effects from taking shape.
The laser beam is supplied by a movable rotary head and plane mirrors allowing for a maximum reflection of 1064 nm. The cleaning head moves along 2 axes: the X axis and the Y axis. The cleaning head can move along a 575mm X axis and a 420mm Y axis.
At the rotary head, the beam is redirected to the mold (Z axis). One specificity resides in the movable head because it allows the laser beam to reach the mold with an incidence of approximately 15° around axis Z.
Different cleaning methods can be used, depending on the type of mold and dirt levels. The cleaning modes are:
- “Rotating cleaning”: To clean with all orientations of the beam,
- “Head stuck cleaning”: To clean with a fixed and predefined orientation,
- “Cleaning followed trajectory”: The orientation of the head follows the path, ideal for cleaning the bottom of a groove with precision,
- “Cleaning + 90 ° trajectory followed”: The orientation of the head cleans accurately one side of a groove,
- “Cleaning path -90 ° followed”: the orientation of the head cleans precisely the second side of a groove.
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MLC 500 machine |
MLC500 Characterictics
- Safe class 1 laser in a closed enclosure, no chemical additive, no projection risk, possibility to work safely as close as possible to the machine
- Pre-programming of the laser path via DXF file (CAD drawings)
- 12.1’’ control screen
- Electric power: voltage/frequency depending on countries, 20A
- Meets CE and FDA standards
- Maximum mold dimensions: 690 X 505 X 150 mm (L x l x h) / 27.16’’ x 19.88’’ x 5.90’’
- Maximum cleaning usable area: 575 x 410 mm / 22,63’’ x 16,14’’
- Maximum mold weight: 180Kg / 396 lbs
- Mobile machine mounted on wheels
- Cooling unit in option
Examples
Laser cleaning can be used to clean rubber and gas fouling, to remove demolding/release agents fouling and also to remove the corrosion of the mold, without damaging the surface treatments of the molds.
Process parameters to achieve for a good and quick cleaning are first the cleaning method, and then
the laser power and the laser speed displacement.
O’Ring mold 150 cavities
- Mold 500x500 mm, 2 plates
- Steel: C45
- Type of fouling: EPDM rubber
- Cleaning method: rotating cleaning
- Laser speed: 12 mm/s
- Laser power: 13 W
- Cleaning time for the 2 plates: 30’
Metal/rubber part mold 8 cavities
- Mold 510x630 mm
- Steel: stainless steel
- Type of fouling: rubber + release agent fouling
- Cleaning method: rotating cleaning
- Laser speed: 50 mm/s
- Laser power: 13 W
- Cleaning time for the whole cavity plate: 11’
Conclusion
Laser has the advantage of being a reliable, quick, safe, and ecofriendly solution with a quick return on investment for mold cleaning:
- Reduced operating cost:
no consumable
automatic cycle, reduced manpower
- Reduced production shutdown times:
no need to cool down and heat again the molds
possibility to program a faster cycle by cleaning only some dedicated and fouled areas and therefore to space out the complete cleaning of the mold
- Reduced installation costs:
No chemical materials to handle and secure
Silent, therefore no need to have protection against noise
Compact and mobile, low floor space requirement
