A part that spends 22 s in a closed mould and needs 15 s of hand loading runs at about a 40 s cycle on one station. With a second station, loading overlaps moulding and the cycle falls to about 27 s, roughly 48% more parts per hour. In a shuttle table vs rotary table choice, that overlap is what you are paying for.
The full calculation is in the worked example below. The sections explain how each table works, when the overlap disappears and what a second station costs you.
Key Takeaways
- A shuttle or rotary table lets one lower mould half be unloaded and loaded while the other is being moulded.
- The gain comes only from loading time; injection, holding and cooling still run in full on every shot.
- A second lower mould half adds tooling cost and needs close matching with the first, so the loading time saved has to repay it.
- A machine waiting for an operator still draws power, so idle loading time costs energy as well as output.
How Does a Shuttle or Rotary Table Save Cycle Time?
It runs two mould halves in parallel. While one lower half sits under the clamp being injected and cooled, the operator or robot unloads finished parts and loads fresh inserts into the other. When the shot ends, the table moves and the prepared half goes straight in.
PlasticsToday describes conventional shuttle tooling as one top A half and two bottom B halves, with the operator loading one B half while the press moulds the other. The aPriori costing guide describes the same principle: pick and place happens on one mould while the other is injected, which can reduce cycle time and labour time.
The saving is the loading time, not the moulding time. Injection, holding and cooling still happen in full on every shot. A table hides the loading inside them; it cannot shorten them. If cooling takes most of the cycle and loading takes a few seconds, the gain is small.
Count the work per shot, not per part. Two cavities with two inserts each means four inserts to place, two finished parts to remove and every pocket to check before the table moves. That total, timed on the real part, is the number to compare with the closed-mould time.
Shuttle Table vs Rotary Table: Which Suits Your Part?
A shuttle table slides two lower halves side to side and suits two-station work with moderate loading. A rotary table turns two or more halves through fixed positions, which suits repeated loading, extra stations and robot loading, at the cost of more floor space and a larger table.
Shuttle table vs rotary table compared with a single-station machine
| Point | Single station | Shuttle table | Rotary table |
|---|---|---|---|
| Lower mould halves | One | Two | Two or more |
| Loading happens | Inside the mould area, while the mould is open | At two positions, one on each side | At one fixed position |
| Operator movement | None between shots | Walks between sides, or one person or robot per side | Stays in one place |
| Floor space | Smallest | Wider, for side travel | Larger, for the table diameter |
| Best fit | Few inserts, long cooling | Two-station work, moderate loading | Many inserts, long loading, robot loading |
The loading position is the practical difference. On a side-to-side shuttle the two loading points sit on opposite sides, so one operator walks between them or the cell needs a person or robot on each side. On a rotary table the load point stays fixed, which makes a single robot or operator easier to plan around.
Tables are usually fitted to vertical clamps, where the lower half lies flat and inserts stay in place by gravity. The aPriori guide treats shuttle and rotary tables as vertical-machine options and models horizontal insert machines with no table.
Either table puts the operator close to moving steel, so guarding at the loading point is part of the design. Light curtains, interlocked guards or two-hand starts are options to agree with the supplier before the layout is fixed.
When Does a Second Station Not Pay Off?
When loading already fits inside the mould-open time, when cooling dominates and loading is short, or when volumes are too low to repay a second lower half. It also loses value if parts must cool in the clamp, because the table cannot move until the part has set.
PlasticsToday notes this drawback of the conventional shuttle: the machine must wait for the first part to cool in the clamp before it can mould the second. If loading takes only a few seconds, the second station mostly adds tooling cost, mould matching and table upkeep.
Tooling is the cost to weigh. The aPriori guide assumes two lower halves and one upper half for a shuttle or rotary table, so one lower half can be loaded while the other is injected with the upper half, and it notes that this choice drives tooling cost.
Waiting has an energy cost too. A PlasticsToday article by Robin Kent reports idling machines drawing 52% to 97.5% of full moulding energy. In Maharashtra, MERC intended kVAh billing for all HT consumers and LT consumers above 20 kW from 1 April 2020, so a pump running while an operator loads inserts shows up on every MSEDCL bill.
Our view: buy the second station for loading time you can measure with a stopwatch, not for a cycle you hope to reach. Time ten shots of loading on the real part before deciding.
How Should You Size a Two-Station Machine?
Time the unloading, loading and checking per shot, and get the closed-mould time from your mould maker or a trial. If loading takes longer than the closed-mould time, the operator or robot sets the cycle and needs speeding up as well. See the 100 ton special purpose injection moulding machine page.
Frequently Asked Questions About Shuttle and Rotary Tables
Does a rotary table need more than two lower mould halves?
Not necessarily. A rotary table can run two halves, but it can also carry three or four, giving extra stations for cooling outside the clamp, checking or a second loading step. Each extra half adds tooling cost and must match the upper half closely, so add stations only for a job you can name.
Can a shuttle table be used with a robot?
Yes. A robot can unload and load each station, but on a side-to-side shuttle the two loading points sit on opposite sides, so the cell needs either a robot that reaches both or one robot per side. Plan the robot layout and guarding before choosing the table type.
Do both lower mould halves have to be identical?
They must make the same part within tolerance, so cavities, insert pockets, cooling and ejection should match. Small differences show up as part variation that alternates shot by shot. Mark each half, track which one made each part, and check both halves during first-off approval.
Is a two-station table only for vertical machines?
Tables are most common on vertical clamps, where the lower mould half lies flat and inserts sit in place by gravity. Horizontal machines usually run one mould and rely on a robot or the operator to place inserts. Costing models such as aPriori treat shuttle and rotary tables as vertical-machine features.
How much floor space does a rotary table need?
More than a single-station machine of the same tonnage, because the table diameter and the loading position sit in front of the clamp. Ask for a layout drawing showing the table, guarding, operator position and any robot reach, and check access for mould changes before fixing the machine's place.
Related Articles
- Special Purpose vs Standard Injection Moulding Machine: How to Decide
- Metal Insert Moulding Around Terminals, Pins and Bushes: What the Machine Needs
- Building an Injection Moulding Cell: Robot, Sorting and In-Line Checking
Sources & References
- PlasticsToday: Shuttle table increases production
- aPriori Technologies, Cost Model Guide: Insert Injection Molding Options
- PlasticsToday, R. Kent: Getting to know your real energy use and cost
- Maharashtra State Electricity Distribution Co. Ltd (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.
Limitation of Liability: Pratishna Engineers makes no representation or warranty, express or implied, regarding the completeness, accuracy or suitability of the information for any particular application. To the extent permitted by applicable law, Pratishna Engineers shall not be liable for any loss, damage, cost or consequence arising from reliance on or use of the information contained in this document. Final machine selection, configuration and application suitability should be confirmed with Pratishna Engineers based on complete and accurate project requirements.
