Take a two-cavity insert job with 24 s of clamp-closed time and 20 s of loading and unloading. With a fixed lower mould half, the cycle is 44 s. On a double-slide table, where one lower half is loaded while the other is moulded, it falls to about 26.5 s. That is a sliding mould cycle time saving of roughly 40%.
The rule behind it is short. A double slide saves the shorter of the closed time and the loading time, minus the time the table takes to move. A single slide, with one lower half that travels out and back, saves nothing and adds two moves per cycle.
Key Takeaways
- Saving per cycle with a double slide = the shorter of clamp-closed time and loading time, minus one table move.
- The saving peaks when loading takes about as long as the closed part of the cycle, and shrinks when loading is quick.
- A single slide improves access and safety but lengthens the cycle; it is not a time saver.
- A second lower half doubles that part of the tooling, and cooling still happens inside the clamp, so price both before committing.
What is a sliding mould on a vertical machine?
A sliding mould uses a lower platen that moves sideways out of the clamp area. With a single slide, one lower half slides out for loading and back for moulding. With a double slide, two lower halves share one upper half and alternate, so loading and moulding overlap.
The double slide is the shuttle table described in trade literature: one top half and two bottom halves, with the operator loading one bottom half while the press moulds the other. A rotary table extends the idea to two or more lower halves on a turntable. A published cost model treats both the same way: pick and place on one mould while the other is injected, cutting cycle and labour time.
Lower platen options for insert work on a vertical machine
| Option | Lower halves | Effect on cycle |
|---|---|---|
| Fixed | 1 | Loading and moulding happen one after the other |
| Single slide | 1 | Same as fixed, plus a move out and a move back every cycle |
| Double slide (shuttle) | 2 | Loading overlaps moulding; one table move per cycle |
| Rotary table | 2 or more | Loading overlaps moulding; can add stations for cooling or inspection |
How do you calculate the sliding mould cycle time saving?
Fixed cycle equals clamp-closed time plus loading time. Double-slide cycle equals the longer of the two, plus one table move. So the saving equals the shorter of closed time and loading time, minus the move. Measure both times on the real job before deciding.
The table holds closed time at 24 s and the table move at 2.5 s, both assumed, and changes only the loading time. Quick loading leaves little to overlap. Loading that matches the closed time gives the biggest gain. Loading longer than the closed time still saves, but the operator now sets the pace.
Cycle saving by loading time (closed time 24 s, table move 2.5 s, assumed)
| Loading time | Fixed cycle | Double slide | Saving |
|---|---|---|---|
| 6 s | 30 s | 26.5 s | 3.5 s (11.7%) |
| 12 s | 36 s | 26.5 s | 9.5 s (26.4%) |
| 20 s | 44 s | 26.5 s | 17.5 s (39.8%) |
| 24 s | 48 s | 26.5 s | 21.5 s (44.8%) |
| 32 s | 56 s | 34.5 s | 21.5 s (38.4%) |
Time the move as well. Table travel, locking and the safety check before the clamp closes all sit inside that figure, and on a short cycle one extra second changes the answer. If the job may later move to automated loading, run the sum again with the robot's time, because a faster loader shrinks the overlap a double slide can win.
When does a single slide make the cycle slower?
Always, if you count only time. A single slide moves the one lower half out for loading and back for moulding, so every cycle carries two table moves on top of the fixed-mould cycle. You buy access, visibility and safety, not output.
On the worked example below, a 2.5 s move each way turns a 44 s fixed cycle into 49 s, which is about 10% fewer parts every hour. That access can still be worth having. Bulky inserts, cables or deep cores are easier to load with the lower half clear of the upper platen, and the operator never reaches under the clamp. Our flat view: choose a single slide for access, a double slide for output, and do not expect the first to deliver the second.
What does a double slide cost beyond the table?
It needs a second lower mould half matched to the first, so that part of the tooling cost roughly doubles. Both halves must locate, heat and cool alike, or the two sides produce different parts. Cooling still happens inside the clamp, so the slide cannot shorten it.
Trade literature names that last point as the main drawback of conventional shuttle tables: the press still waits for each part to cool in the clamp. The aPriori cost model also flags that the number of lower and upper halves drives tooling cost. Mark each lower half and track rejects per half, so a fault in one side is caught early.
There is an energy angle too. Measurements reported in PlasticsToday found idling machines drawing 52% to 97.5% of their full moulding energy, so a press waiting for the operator still runs the meter. In Maharashtra, MSEDCL charges demand on kVA and energy on kVAh, a billing basis MERC set for HT consumers and LT consumers above 20 kW from April 2020, so a lightly loaded motor running at poor power factor during that wait adds to the bill as well.
What should you measure before choosing a sliding table?
Time 20 or more real cycles and split each into clamp-closed time and loading time, then send those figures with the part drawing, insert count and cavity plan. See the vertical clamp insert moulding machines page for the fixed and sliding table options this data is matched against.
Frequently Asked Questions About Sliding Mould Cycle Time
Does a sliding table shorten cooling time?
No. Cooling happens while the mould is clamped, and a sliding table does not change that. What a double slide removes is the wait while the operator unloads parts and loads inserts, because that work moves to the second lower half while the first is in the clamp.
Is a rotary table better than a double slide?
It depends on the job. A rotary table can carry two or more lower halves, so it can add a station for inspection or extra cooling, and the operator stays in one place. A double slide is simpler, with two halves moving side to side. Compare both on the measured cycle.
Can one operator run a double-slide machine?
Yes, the layout is built for that. The operator unloads and reloads one lower half while the other is moulding, then the table swaps. If loading takes longer than the clamp-closed time, the operator becomes the pace setter and the press waits, so check the timing first.
Do both lower mould halves need to be identical?
They should be. Both must locate inserts in the same positions, heat and cool alike and close on the same upper half without mismatch. Differences show up as two families of parts. Marking each half and tracking rejects separately makes it easy to see which side drifts.
When is a fixed lower half the better choice?
When loading is quick compared with the clamp-closed time. With a 24 s closed time and 6 s of loading, a double slide saves only about 3.5 s per cycle, which may not justify a second lower half. A fixed half is also simpler for short runs and frequent mould changes.
Related Articles
- Insert Moulding on PVDL Vertical Clamp Machines: Setup and Loading
- Moulding Plug Tops With Brass Pins on a Vertical Machine
- Threaded Brass Inserts in Plastic Parts: Moulding and Pull-Out Strength
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.
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