Aluminum Mold Damages – Structural Support Solutions
Written by admin, 24 March 2021
In my opinion, the designer of steel fabrication of a support for a large aluminum casting mold must answer to challenges created by known goals that will also include aluminum repair. And he/she should find the answers where damages to the large aluminum mold have happened. It helps a lot if you can notice “the devil in the details” in the aluminum casting mold, but sometimes the “devil looks at you right in the eyes”. In my opinion, the good designer for steel support should have a keen eye to both a “big picture” and a “detailed picture” point of view. Especially, the aluminum repairs will benefit from a more detailed picture.
When creating a new support structure or improving an old support structure a one thing have to be absolutely clear. Avoid at all cost causing more damages to aluminum casting mold and use innovations that provide solutions to as many problems as possible. The idea is that one innovation should resolve as many problems as possible and it should not create any more problems since aluminum repairs are both risky and costly.
Problems evaluation and solutions for aluminum mold damages
Aluminum mold lid bowing problem
First, I have measured the deflection of the old aluminum casting mold’s lid structure when lifted with the jig. The deflection of the old lid that contained the engagement plates was 3.5 inches in the middle of the steel structure. At each end the deflection was about 2.5 inches. The initial conclusion was clear, the aluminum cast mold’s lid has bowed along its length of about 16 feet. The steel ½” treaded rods have enforced the bowing force. I knew back then that I have to reduce this bowing issue by removing the heavy engagement plates.
The discovery of a wrong engineering assumption
At that time however, I was convinced that this aluminum casting mold’s lid also causes these deflections. I also believed that the steel structure provides the resistance to the aluminum cast lid. Oh, boy I was wrong. First, we have removed the old steel structure by cutting treaded rods. Second, we have lifted the steel structure of the aluminum casting mold’s lid. Then we have measured the deflections once again. The deflection of the bow in the middle has increased to 9.5 inches and the deflection of both ends was 7”. Wow! This was surprising.
The only logical conclusion was that the aluminum mold lid has actually reduced the deflection of the whole steel structure. And the steel support that supposed to help the aluminum lid maintain the shape was actually causing the damages.
Very clear objectives for the new steel support
Therefore, two issues become obvious right away:
- I had to remove the heavy engagement plates from each end of the lid and
- I had to design the top steel support in very simplistic way that will maintain the structural strength of steel elements. This steel support structure should provide ridged support tor the aluminum mold lid.
Removing the heavy engagement plates from the lid structure was relatively easy. I knew that I would be able to attach them back to the bottom structure of aluminum mold. However, bowing elimination of the steel in both structures, the lid structure and the bottom’s structure, have required some thought.
The single steel element will always bow at the length of 19 feet. But, the enclosed steel structure in the same space would reduce the bow deflection. Therefore, I had to design and then use best welding practices to fabricate an enclosed steel structure. More specifically, I had to fabricate 2 enclosed structures, one for the lid and one for the bottom mold. These enclosed structures would involve
- Long HSS elements going through the whole structure length (A , D)
- HSS tube rim following the aluminum mold shape and (B, E)
- HSS elements joining the long HSS elements with the HSS tube rim (C, F)
- Mounting plates welded to the bottom structure (G)
- Improvement to rigidity in incline position (element H)
Disengagement of bottom mold’s steel structure in the cooler problem
When the old unit was put to the cooler, the bottom mold’s support structure was disengaging from the top structure. The disengagement have created the gap about 1- ¾ ”. Additionally, during rotation at about 10 rpm the bottom mold’s steel support was dragging at the 90° position at about 1”. I had to use the estimate here since the whole unit was rotating pretty fast and I was not able to measure the drag more precisely.
To tackle this issue, I have implemented the space steel structure concept with enforcements of positioners. Moreover, I have introduced pins to lock both structures together, the lid’s structure together with bottom mold’s structure, within a tolerance of 1/16 inch. This has been a significant and simple innovation.
The solution to counteract disengagement and lid bowing correlation
I decided that I must positively joint the bottom mold support with a lid support in a simple rectangular prism or cuboid. This rectangular prism should have dimensions about 19’x 3’x3’. Please keep in mind that the actual dimensions were slightly different. I have intended to relocate the walls 3’x 3’ with heavy engagement plates to the bottom support structure. The positioners and pins were enforcing rigidity between structures and pins were locking these structures together during rotation and inclines.
I thought that simple rectangular cuboid in closed position should provide maximum resistance to the deflection forces damaging the aluminum cast and steel structure that supports it. ….And I was right. After we have finished the steel fabrication of the mold’s lid support, the deflection at each end was 0.5 inch. And, the aluminum mold lid comfortably straightened out. Most importantly, the whole rectangular prism deflection after positive engagement was 9/16” at both ends. Additionally, we did not observe of any disengagement of bottom mold’s support and we did not see any dragging effect when the whole unit landed in the dyer.
Aluminum Mold damages – detailed point of view
Bowing of “flats”
Clearly the position old clamps were causing the bowing of both flats that is the flat of the lid and the flat of the bottom mold. Therefore, when technicians increase the tension of these clamps than the clamps have caused more bowing of the flats. The clamps position has amplified the problem additionally due to the leverage of the element B.
The solution to the issue was relatively simple. I had to position the clamps parallel to the structure to eliminate the angular force acting on the steel structure. Also, I wanted to eliminate the element C completely. Fortunately, the main concept of closed cuboid with a enclosed structures on top and the bottom have suited my intentions very well.
Damaged aluminum cast step – ups
The damages of step-ups in the aluminum cast that accommodated the treads for the treaded rods were very significant. These step ups were too shallow anyway for a full support of the threaded steel rod.
Damages of treads in aluminum bores of the mold’s lid
These damages were so severe that the aluminum mold lid was at risk of disengagement from its steel support. The form maker lifts the whole almost 19 feet structure using a crane and a lifting jig attached to the lifting points of the lid’s steel structure. Therefore, the situation has become rather hazardous since disengagement of threaded rods from the lid would cause the fall of the whole structure. The 3561-aluminum alloy used for this aluminum mold is a rather soft alloy and the hazard was clear.
I had no choice but to replace the step – ups of the lid with aluminum cuboids that would be welded to the lid. The design involved machining of much taller 3561 aluminum cuboids with the tapped thread. The planned cuboid were 1 inch taller that original step-ups. I intended to install non-removable ½” threaded rod into the aluminum cuboid and then weld the cuboid to the mold’s lid. As simple as it sounds, obviously the plan contained two rather risky tasks:
- Machining of 3561 aluminum cuboids
- Welding of cuboids to the aluminum mold’s lid
You can find the description of welding cuboids in “Aluminum Welding of 3561 Casting Alloy” and machining of cuboids in “Custom Metal Fabrication” article.
Damages of tread in aluminum bores of the mold’s bottom
These damages were much smaller in comparison to damages in upper lid. The bottom mold have not experienced any separate lifting by itself since it has always joined with the lid during the lifting task. However, the bottom mold has experienced significant dragging and disengagement effect in the oven and in the cooler that is why some of many of these threaded rods were moving perpendicularly to the cast. The distance between the step-ups and the first rigid point was very significant providing excessive leverage for the perpendicular movement. Overall, the bottom support steel structure was a complete designing failure.
If the perpendicular movement has already damaged the thread in the step-ups, I was planning to repair it with helicoil or replace the step-ups.
I have never intended to weld the cuboid to the vertical surface of the mold. This vertical wall has had was a working surface inside the mold. And, I was not prepared to take the risk of possibly damaging the mold’s working surface. Any damage to the cuboid welded to the outside of the vertical wall, would damage the working surface. And this was the risk I wanted to avoid at all cost.
In addition, I knew that the new structure for the bottom’s mold would be rigidly attached to the lid structure. This rather ridged attachment would eliminate the dragging and disengagement. The planned positioners would only have 1/16 inch tolerance and the pins that would provide locking effect had also only 1/16 tolerance. Moreover, I was planning to introduce elements counteracting the incline of 25° on both sides of molds bottom’s support structure.
Introduction of high-power Italian clamps aluminum cast mold
Since the old clamps were in the disintegration stage, I have planned to utilize new more powerful clamps with comfortable regulations. The search and sourcing of good quality and heavy industrial clamps is not so easy. Fortunately, friends from Jwwinco have step up with their selection. The testing of Italian clamps left long lasting positive impression. Therefore, we have settled on the Italian 4000 lbs clamps. You can read about our testing in “Custom Metal Fabrication – Preparation Stage”
The increased support for clamps
3My structural design involved fabrication of HSS rim following the shape of the mold. I knew that this will be a very complicated fabrication since it would involve cuts in two angles at specific points at both sides of element. These elements then would have to be welded to form the rim.
Additionally, I wanted the rim to have a maximum contact with the welded cuboid for the best transfer of clamps’ force into the mold. Therefore, I had to design the element that would meet following conditions:
- Provide the best transfer of force from the HSS rim to the mold
- Allow for angular imperfections of the HSS rim and still provide full contact with the cuboid
- Allow for welding of clamp’s latch with a tolerance of ½ inch
- Comfortable to weld in these conditions and simple to fabricate.
A simple drilled angle and a plate positioned on top of the cuboid have met my conditions. The use of angles has allowed me to completely remove the gap between the rim and the step up or between the rim and the new aluminum cuboid.
Elimination of twist
Additionally, I was planning to fabricate the structure that will prohibit angular twisting of bottom and top rims. I have intended to achieve this objective by properly position the clamps. The close position of HSS rim to the step-ups and cuboids have reduced the forces acting on aluminum bores by significantly reducing the leverages. More importantly, these rims would also eliminate the twisting effect of high-power clamps. Each HSS rim will be supported by additional structure prohibiting the twist.
Effort to eliminate opening clamps in the oven
Moreover, I was planning to position the clamps on the slightly higher plane in comparison to their latches to prohibit clamp opening in the oven. Testing in the shop have provided guidance for this fabrication.
In summary to solutions for aluminum mold’s damages
My designs have provided the solutions to all causes of the aluminum mold’s damages. Since I did not want to increase cost of the steel fabrication, I have made simple sketches of each element with simple comments what to watch for during the steel fabrication. Therefore, a technical drawing has never been made and the whole fabrication was made based on manual sketches. Wow, this must be very surprising to you, but this is the truth.
I also wrote a reminder for myself and for the other welder regarding good welding practices for this project. The reminder included machine setups parameters and mold position during the fabrication. The mold position, the closed position of the lid on top of the bottom, was always enforced by C-clamps. Therefore, the steel structure supporting the mold’s lid has been fabricated when the long gap of 4.5 feet between lid and bottom mold has been almost completely eliminated.