Lower mould arrangements on a sliding table vertical machine compared
| Arrangement | How it works | Cycle time | When it fits |
|---|---|---|---|
| Fixed lower mould | Lower half stays under the clamp; inserts are loaded in place | Closed time + loading | Few inserts, short loading |
| Single slide | One lower half slides out to a loading station and back | Closed time + loading + two moves | Heavy or tall inserts; access and visibility |
| Double slide (shuttle) | Two lower halves share one upper half; one is loaded while the other moulds | Longer of closed time and loading, + one move | Loading close to or above closed time |
| Rotary table | Two or more lower halves on a turntable | As for double slide | Extra stations for unloading, checking or robot loading |
Use a sliding mould on an 80 t vertical machine when insert loading takes long enough to matter, or when the operator should not reach under the upper mould. A single slide improves access; only a double slide, with two lower halves, lets loading overlap moulding and lifts output.
Key Takeaways
- A single slide moves loading out from under the upper mould but adds two table moves to every cycle.
- A double slide uses one upper half and two lower halves, so the second lower half is extra tooling cost.
- Each lower half still stays in the clamp until its parts cool, so a double slide removes loading time from the cycle, not cooling time.
- A machine waiting for loading still draws power, and under MSEDCL kVAh billing that energy is charged like any other.
What Does a Sliding Table Vertical Machine Change?
Where the operator works. On a fixed lower mould, inserts go in under the open upper half. On a sliding table, the lower half travels out to a loading station, so loading happens in the open, away from the clamp, and the half slides back for the shot.
Out at the station, the operator can see every pocket, use both hands and handle heavier inserts or a loading fixture. There is also room to mount a sensor or camera that checks the inserts before the half goes back in.
The cost is time and accuracy. Each slide out and back adds seconds to the cycle, and the lower half must return to the same position every time so the guide pillars engage cleanly. Worn slides or loose stops show up as parting-line mismatch and wear on the guides.
Which Insert Jobs Suit a Single Slide?
Jobs where the inserts are heavy, tall or awkward to place, where a loading fixture or several insert sizes need a clear view, and where volume does not justify a second lower half. The single slide buys access and a safer loading position, at the price of slower cycles.
Examples include a housing that takes a busbar or a large bush, a part with long pins standing in the lower mould, and an overmoulded sub-assembly that has to be set into a nest by hand. In each case, loading under the open upper half is slow and leaves little room for the hands.
The table itself needs guarding. A moving lower half is a pinch point of its own, so the loading station needs guards, and the slide should start only when the operator's hands are clear. Agree the guarding with the machine supplier at the order stage, not after installation.
When Does a Second Lower Mould Pay Off?
When loading takes about as long as moulding. With two lower halves, one is loaded at the station while the other moulds, so the cycle becomes the longer of the two plus one table move. When loading is short, the second half adds tooling cost and little output.
PlasticsToday describes the conventional shuttle table for insert work as one top half and two bottom halves, with the operator loading one while the press moulds the other. It also names the limit: the machine still waits for each part to cool in the clamp before moulding the next.
A cost model from aPriori treats the shuttle and the rotary table the same way. Either lets pick and place happen on one lower half while the other is injected, which can cut cycle and labour time, and the default of two lower halves plus one upper half drives the tooling cost.
Our view: buy a single slide for access and safety, and a double slide for output. Do not expect a single slide to raise output, because it adds table travel to every shot.
What Does Waiting for the Operator Cost in Power?
More than the idle time suggests. A machine waiting with the mould open still runs its heaters and, on a hydraulic machine, its pump motor. Moving loading out of the cycle cuts the idle energy behind each good part as well as raising output per hour.
A PlasticsToday study by Robin Kent found idling machines drawing 52% to 97.5% of their full moulding energy, and one idling at 64%. A clamp-meter data logger can measure a machine in as little as 30 minutes, so measure energy per good part before and after the change.
In Maharashtra, MSEDCL bills demand in kVA and energy in kVAh. Its FAQ notes that at a power factor of 0.85, 15% of the power does no useful work, and it recommends capacitors or APFC panels. Idle draw billed in kVAh at a poor power factor costs more than its kWh suggests, so fix the power factor as well as the waiting.
How Should You Decide for Your Insert Job?
Time the loading routine on a trial fixture, estimate the mould-closed time from the wall thickness and resin, and compare the two. If loading is short, stay with a fixed half. If access is the problem, use a single slide. If loading nearly matches moulding, price a double slide. See the 80 ton vertical injection moulding machine page.
Frequently Asked Questions About Sliding Moulds on Vertical Machines
Is a rotary table better than a double slide?
Not always. A rotary table can carry more than two lower halves, which leaves room for separate unloading, checking and loading stations or a robot. A double slide is simpler and needs only two halves. Choose by how many steps happen outside the clamp and the space around the machine.
Do the two lower halves have to be identical?
Yes, as near as the toolroom can make them: the same cavities, shut-offs, ejection and cooling. Any difference shows as part variation between halves. Mark each half's parts, for example with a small cavity number, so a fault can be traced to the right half.
Does a sliding table change the clamp calculation?
No. Only one lower half is under the clamp at a time, so the clamp is worked out from the projected area of the cavities in one half plus any runner. The applications article in this series shows the method and the area limits at 80 t.
How can loading time be measured before the mould exists?
Build a simple plate with pockets in the planned layout and time an operator placing real inserts from the way they will be supplied. Repeat it enough times to see the spread, and add part removal and a cavity check. Use the longer figures for planning.
Can a single slide be converted to a double slide later?
Sometimes, but plan for it at the start. A double slide needs table travel to both sides, a second loading station, guarding and controls for two halves. Check those with the machine supplier before ordering a single-slide machine if a second half is likely within a few years.
Related Articles
- What Can You Make on an 80 Ton Vertical Insert Moulding Machine?
- Multi-Insert Housings on an 80 Ton Vertical Machine
- Automotive Insert-Moulded Parts on Vertical Machines
Sources & References
- PlasticsToday: Shuttle table increases production (Aug 2008)
- aPriori Cost Model Guide: Insert Injection Molding Options
- PlasticsToday, R. Kent: Getting to know your real energy use and cost (Jan 2010)
- MSEDCL: kVAh Billing: Frequently Asked Questions
Technical Disclaimer
Disclaimer: The information provided in this document is for general informational and educational purposes only. It is based on technical references and industry information available at the time of preparation and may be subject to change. It does not constitute engineering, technical, commercial or professional advice, nor does it constitute a quotation, specification, warranty or contractual commitment by Pratishna Engineers.
Actual injection moulding machine and process requirements vary according to the component design, material, mould, production volume, machine configuration and operating conditions. The information, examples, calculations and recommendations provided should be independently evaluated and verified for the specific application before making any equipment, process or production decision. Information obtained from third-party sources remains subject to the accuracy and limitations of those sources.
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