When you’re preparing to add an automated no-bake molding system, there are a number of critical decisions to be made that require careful analysis. As with many design projects, the end of the process is often the best starting point. It’s a basic concept to design backwards, at all times keeping in mind the molding process results you expect.
There are dozens of criteria that go into a well designed system, but a few of the main considerations are: mold rate per shift; mold size minimum and maximum; budget available; floor space available; staffing requirements/cost; complexity of coring; resin system; reclamation system requirements; engineering requirements; installation requirements; and time available for installation / commissioning.
Often we’ll ask foundries what their desired mold count is, and we get a one-word answer: “more.” “More” is not a number, but that number must be determined as it is the primary driver for the design of any system. The mold rate must be established at the beginning of the design phase. It can be changed throughout the course of the system design, but a well-defined production rate is a critical decision.
In a typical no-bake jobbing foundry, the work changes constantly. Mold size, complexity, quality, and alloys all change fairly often, which makes designing the molding system a challenge. If all or most of the variables are understood upfront, designing a flexible system is far easier than adjusting a system later.
For some requirements and budgets, a simple mixer/conveyor/mold handler set-up will be sufficient. At the other end of the spectrum, a fully automated system — including sand storage, mixing, molding, cooling, reclamation (both mechanical and thermal), automated casting cleaning, and inspection with first op machining — may be required. There is an extraordinary range of design possibilities between these two types of molding systems.
Parallel Conveyor Systems — Most metalcasters are familiar with the traditional, parallel conveyor loop set-up with transfer cars at each end, but there are a number of modern designs that also deserve consideration. The parallel conveyor system is a well-established process, with various iterations of the basic design installed throughout the world. It is flexible and can accommodate a wide variety of mold sizes and production rates.
Still, this design takes up quite a bit of floor space compared to other designs, and can be more expensive. These designs are fairly complex, too: a fully automated system includes a number of motor starters, proximity sensors and programming requirements.
If a foundry has to carry out a great deal of mold prep work, a conveyor-based system can be a good choice because the prep area/length can be set to whatever the operating conditions require.
Carousel Systems — Carousel based systems are very popular and logical for small to medium-sized molding (up to 60x60x30/30) requirements. Over 90% of the molding systems Palmer has designed in the past 20 years have had some type of carousel design. Significant benefits are the comparatively low capital costs, reduced floor space requirements, and operational simplicity.
With a rollover cycle rate of 90 seconds, a production rate of 20 molds/hour is achievable. Larger molds up to 60x60 require a longer rollover cycle time (approximately 2 minutes), resulting in a mold production rate of 15 molds per hour.
These rates are accomplished with essentially one moving part: the carousel has a gravity roller conveyor on board with high-quality rollers. The empty boxes are rolled off the carousel manually, filled, compacted, struck off, and returned to the carousel in less than the cycle time of the rollover. This is achieved with only one drive and a few proximity switches. Compared to a multi-zone power roller-based system, this is a much simpler system, in terms of operations and maintenance. (Please note that all production rates are for production of copes/drags only, and do not include downstream process such as coating, drying, coring, closing, or clamping.)
New Molding Technologies
Current technologies in molding production eliminate the need for an expensive rollover, which accelerates the molding process considerably. Rollovers are expensive and limit the maximum mold height to the daylight available in the rollover. With barrel style rollovers both the height and the width of the mold are limited.
C-frame rollovers give flexibility on width but also limit height. In the Palmer Universal Molding Machine™ (UMM) systems no rollover is required and daylight is essentially unlimited, at no additional system cost or production rate change.
Green sand to no-bake molding system — The basic Palmer UMM rotary molding system is designed to use existing green sand or no-bake tooling to produce no-bake molds at a rate of 20 per hour, in sizes from 12x12x4/4 to 26x36x20/20 with one operator.
Other UMM sizes are producing at rates that are equal to or close to automatic green-sand molding machine production rates of 65 molds per hour, in sizes from 12x12x4/4 to 36x36x12/12, with two or three operators, depending on the design.
Existing green-sand matchplate machines have simple wooden boxes mounted to them and cope-and-drag boxed work is mounted back-to-back on the tooling frames (essentially, a matchplate design.) After the boxes are filled, compacted, and struck off, they are indexed. As a filled box is indexed toward the fill station, it is inverted. A precision scissors lift rises to the inverted mold surface, which receives the mold half and lowers while the opposite half is being made.
As soon as the scissors lift is in the down position, the conveyor on top starts running the mold half out to the mold prep area. This allows for any amount of daylight desired, at the same cost and with no effect on the mold production rate.
Larger UMM systems have been produced in sizes up to 60x60x30/30 with production rates of over 20 molds per hour, with one operator – and no rollover!
With this UMM design, cope/drag boxes are mounted on a platen that is isolated from the main machine frame with omnidirectional isolators. This platen is inverted using hydraulic rotary actuators.
Six to eight of these platens are arranged on a carousel system where the box is filled and compacted with an on-board vibrator, indexed, and when the sand sets up inverted, to be drawn with a scissors lift as described above. Again, this design allows for 6 ft or more of daylight without a rollover machine.
Ejection Systems — Mold production systems also are being made so that the mold is filled, compacted and struck off in the normal way, with the sand being blended to set up very quickly and consistently. Once the sand is set, there are ejection pins that push the mold out of the mold box to a point where a simple gripper can grab and index it 180 degrees onto a simple conveyor belt, mold side up.
These systems are almost completely automated with robotic coating, gluing, closing, mounting of the correct pouring basin, and storage; with molds going to the pouring station sorted by alloy, pouring temperature, and cooling time, etc. Finished molds have been produced at rates of 36 seconds per completed, closed mold! That is almost 100 molds/hour with no labor needed until metal is poured into the mold.
Another exciting new technology for automated mold and core production is 3D sand printing. While this technology is currently relegated to prototype and low-production rates, 3D printing using robotic technology can print molds and cores of virtually any size in an unattended system at a very reasonable capital cost.
Because the “printer” is fixed to the end of a robotic arm, the size, height, and complexity of the work is almost unlimited. When a mold is finished, it is simply rolled out of the production area and production starts for the next mold a few seconds later. Cores and molds can be produced singly or in multiples, simply and quickly.
While this technology is somewhat slow in comparison to other techniques, multiple machines can be operated at the same time as the cost per installation is low.
ROI is quite prompt because the mold/core production can be completely unattended, with labor needed only to remove the parts from the loose sand and to prepare them for assembly.
With all the modern no-bake molding technologies available, there is no reason a productive, affordable, profitable system cannot be made to fit every production and budget requirement.
Jack Palmer is president of Palmer Manufacturing & Supply Inc. Visit www.palmermfg.com