A specialist plastics company wanted an automatic system to remove moulding flash, which meant ATM Automation had to meet design, process and health and safety requirements.
When specialist plastics utilities product maker, Polypipe asked ATM Automation to devise an automatic flash removal system for its of blow moulded Ridgigully products, ATM had to cope with design, process and health and safety requirements As part of the Polypipe surface water drainage system, Ridgigully products are blow moulded in high-density polyethylene (HDPE) in three different sizes.
The moulded products have significant amounts of flash around the mould joint line which traditionally, was removed manually.
The largest of these parts weighs up to 12kg and with some areas of flash being up to 12mm thick, the manual flash removal process was time consuming and arduous.
Following a review of various flash removal processes and automation concepts by Polypipe, it chose ATM to provide an automated flash removal system based upon a 6-axis robot and a laser.
ATM was well acquainted with automotive industry laser cutting applications, which are finely toleranced operations demanding precise programming and robot path control.
Such components have clearly defined datum points that allow a laser and robot to easily meet the dimensional and profile tolerances required.
ATM told manufacturingtalk that there were a number of distinct differences between laser cutting automotive projects and the Polypipe products.
The blow moulded part has a larger tolerance band and the material is very different.
* Coping with problems – there were three different sizes of product to be laser cut (300mm, 750mm and 900mm).
Not only had a system to remove flash from the moulding, but it also had to cut two 360 deg paths.
ATM decided that the best approach would be for the robot to hold the part and manipulate it under a fixed laser cutting head.
A 6-axis robot system with a horizontal reach of 2000mm and a payload capacity of 50kg, was chosen to provide the working range and handling capacity required for these large components.
ATM chose Rofin-Baasel UK for the laser system, based upon Rofin’s extensive application experience and the excellent reputation for reliability of Rofin CO2 lasers.
A diffusion cooled slab laser with an output power of 2,5kW, was selected for the project.
Detailed consideration also had to be given to fume extraction and filtration for this project, as the parts being cut are produced from 100% regrind material.
It meant that the blow mouldings can contain a number of contaminants which could have a detrimental impact on the performance of any extraction and filtration system.
Following a series of trials, a multi stage dosing filter system was developed, with the air extracted from the cell being dosed with calcium carbonate before reaching the filtration system.
To minimise the time associated with cleaning filters and removing debris from the filtration system, two sets of filters were incorporated.
This enables one set of filters to perform a self cleaning cycle, depositing any dust and debris in a bin, whilst the system continues to run using the second set of filters.
* Work cell concept – the work-cell concept incorporates two component fixtures at the operator load and unload station.
This enables the robot to deposit a completed part and immediately pick up a new part ensuring minimum time is lost between the laser cutting operations.
With an internal safety door closed to protect the operator, the finished part can be manually removed and another part loaded for processing by the robot.
The robot gripper system and the component location fixtures, incorporate quick change tooling features to enable the system to handle the three different product sizes produced within the cell.
* Meeting tolerance specifications – the dimensional tolerances required flash to be removed from all areas around the mould tool joint line, and in places this flash can be up to 12mm thick.
In addition, to enable the flash being removed to be re-processed more easily, the larger areas of waste material had to be cut into smaller pieces.
This required intricate programming by the ATM engineers to achieve the balance between reducing the size of the waste material and maintaining the target cycle time.
A major issue was the need to produce trimmed components with a minimum of excess material, on components which have potentially large part to part variations in size.
The variation on each component meant that it was not possible to establish a consistent datum position, from which program offsets could be generated, and this led the ATM engineers to develop a highly unusual but extremely effective solution.
In almost every laser application, the beam is focussed to a fine spot, at a particular distance from the nozzle or optics, to generate a small spot size and enable precision processing of the part.
Even with a powerful laser such as the Rofin DC025 a spot size of 1.0mm is achievable at the appropriate focal distance.
This application however did not require such degrees of accuracy, owing to the variations in part tolerance, and ATM turned this to its advantage.
By developing clever programming techniques and using the laser ‘Out of Focus’, a larger spot size was achieved.
Using the laser outside of its focal point would require more laser power to cut the material, and ATM’s initial choice of a 2,5kW laser proved to be a major contributing factor in developing this final solution.
The larger spot size together with the higher power settings on the laser enabled the system to not only achieve the cut profiles required during flash removal, but the high temperatures reached during the trimming operation also partially melt the cut area providing a smooth aesthetic finish on the part.
Polypipe has achieved its objective of turning a labour intensive and arduous task in to a cost effective and highly reliable automated system.
ATM has also clearly demonstrated that difficult and unusual automation applications can become a reality using a combination of field proven hardware lateral thinking, and a determination to satisfy the customer’s requirements.
* About Polypipe – Polypipe Civils is the UK’s leading manufacturer of surface water drainage, sewerage, cable protection systems and water management solutions, serving the utilities, construction, civil engineering, agricultural and sports and leisure markets.
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