Quick Answer
When setting up a new injection molding factory, do not purchase the injection mold and injection molding machine as two independent items.
Before the mold design is finalized, the mold supplier should receive the complete injection molding machine specification, including tie-bar spacing, platen dimensions, mold thickness range, opening stroke, ejector stroke, locating ring size, nozzle radius, shot capacity and available core-pull connections.
At the same time, the machine supplier should receive the expected mold dimensions, part weight, resin, cycle time and production requirements.
The safest approach is to treat the mold, machine, robot, cooling system and material-handling equipment as one complete production cell.
Why Mold and Machine Matching Matters
A mold may be technically well designed but still fail to operate on the customer’s injection molding machine.
Common problems include:
- The mold cannot pass between the tie bars
- The mold is too thick or too thin for the machine
- The machine cannot open far enough for part removal
- The ejector rods do not match the mold ejector plate
- The machine shot capacity is too small
- The locating ring does not fit the machine platen
- The machine nozzle does not seal correctly against the sprue bushing
- Hydraulic core-pull circuits are not available
- The mold is too heavy for the platen or mold-changing equipment
- The robot cannot reach the part safely
- Water, air and electrical connections are positioned incorrectly
These problems can cause mold modification, machine modification, project delays or the purchase of a larger machine than originally planned.
For a new factory, such mistakes are especially costly because several molds and machines may be purchased at the same time.
The project should therefore begin with a compatibility review before either the mold or machine specification is frozen.
The Three Parameters Buyers Most Often Forget
Three machine parameters are especially important and should always be sent to the mold supplier.
1. Tie-Bar Spacing
Tie-bar spacing is the clear horizontal and vertical distance between the machine’s four tie bars.
The mold must physically pass between the tie bars during installation.
For example, if a mold is 900 mm wide but the horizontal tie-bar distance is only 850 mm, the mold cannot be installed through the normal mold-loading direction.
Do not compare tie-bar spacing only with the mold cavity size.
The complete mold width includes:
- Mold plates
- Clamping slots
- Hydraulic cylinders
- Slides
- Connectors
- Water manifolds
- Hot runner plugs
- External mechanisms
A mold that appears suitable based on the plastic part size may still be too wide after these components are added.
Buyers should provide both:
- Horizontal tie-bar distance
- Vertical tie-bar distance
The mold supplier should then confirm the final mold envelope before manufacturing begins.
2. Maximum Opening Stroke
The machine must open far enough to release and remove the molded part.
The required opening is affected by:
- Product depth
- Core depth
- Ejection distance
- Robot gripper thickness
- Sprue length
- Slider movement
- Part-removal direction
- Whether the part drops automatically
- Whether manual removal is required
Maximum opening stroke alone does not tell the complete story.
The buyer should also confirm the machine’s maximum daylight.
Maximum daylight is the total space between the platens when the machine is fully open.
In practical terms:
Maximum daylight = mold installation height plus opening stroke
The available opening space after the mold is installed must be greater than the space required to release the part and remove it safely.
For deep boxes, crates, buckets, automotive panels and products removed by robot, this check is critical.
3. Ejection System
The machine ejector must match the mold’s ejection design.
Important details include:
- Ejector stroke
- Ejector force
- Number of ejector rods
- Ejector rod diameter
- Ejector rod positions
- Ejector plate hole pattern
- Mechanical or hydraulic connection
- Central or multi-point ejection
- Machine ejector return method
A small mold may use one central ejector rod.
A large automotive, crate, pallet or appliance mold may require multiple ejector points to distribute force evenly.
If the machine has only a central ejector but the mold requires several ejector rods, an adapter plate or different ejector arrangement may be required.
The ejector design must be confirmed before the mold back plate is finalized.
The Complete Mold and Machine Compatibility Checklist
The following checklist can be copied into an email, spreadsheet or project specification.
SECTION A — PLASTIC PART INFORMATION
| Item | Information Required | Buyer Input |
|---|---|---|
| Product name | Name and application of the molded part | |
| 3D part drawing | STEP, STP, X_T, IGS or similar format | |
| 2D drawing | Dimensions, tolerances and assembly details | |
| Part dimensions | Length × width × height | |
| Part weight | Estimated or confirmed net weight | |
| Plastic material | PP, ABS, PC/ABS, PA, HDPE or other resin | |
| Filler content | Glass fiber, mineral filler or other reinforcement | |
| Color | Standard color, masterbatch or special appearance | |
| Surface finish | Polished, textured, painted or technical surface | |
| Annual quantity | Expected parts per year | |
| Daily production target | Parts per day or shift | |
| Required cycle time | Target molding cycle | |
| Quality requirements | Tolerance, appearance, assembly and testing requirements | |
| Packaging method | Bulk, tray, carton or automatic packing |
SECTION B — INJECTION MOLD REQUIREMENTS
| Item | Information Required | Buyer Input |
| Number of cavities | Planned cavity quantity | |
| Mold life target | Expected production cycles | |
| Runner system | Cold runner, hot runner or open hot tip | |
| Preferred hot runner brand | If specified | |
| Mold steel | Required grade or supplier recommendation | |
| Mold base standard | DME, HASCO, LKM or customer standard | |
| Gate type | Edge, pin, valve gate, sub-gate or other | |
| Ejection method | Pins, stripper plate, air ejector or hydraulic system | |
| Core-pull requirement | Hydraulic, pneumatic or mechanical | |
| Unscrewing system | Required or not required | |
| Mold change method | Crane, forklift, mold cart or automatic system | |
| Mold lifting direction | Top, side or special orientation | |
| Spare parts required | Inserts, heaters, thermocouples, seals and wear parts | |
| Mold standard | Customer specification or supplier standard | |
| Destination country | For electrical, connector and documentation requirements |
SECTION C — CLAMPING UNIT INFORMATION
| Item | Information Required | Buyer Input |
| Machine brand | Injection molding machine manufacturer | |
| Machine model | Complete model designation | |
| Clamping force | kN or metric tons | |
| Tie-bar spacing | Horizontal × vertical clear distance | |
| Platen dimensions | Width × height | |
| Minimum mold thickness | Minimum mold installation height | |
| Maximum mold thickness | Maximum mold installation height | |
| Maximum opening stroke | Machine platen opening stroke | |
| Maximum daylight | Maximum distance between platens | |
| Mold weight limit | Maximum supported mold weight | |
| Clamping slot dimensions | Slot width, depth and location | |
| Mounting hole pattern | Thread size and hole positions | |
| Quick mold clamp | Available or not available | |
| Mold loading direction | Top or side loading | |
| Safety door opening | Maximum installation clearance |
SECTION D — EJECTION SYSTEM INFORMATION
| Item | Information Required | Buyer Input |
| Ejector type | Mechanical, hydraulic or servo-electric | |
| Maximum ejector stroke | Available ejection travel | |
| Maximum ejector force | Forward and return force | |
| Number of ejector rods | One, multiple or ejector plate | |
| Ejector rod diameter | Machine ejector rod size | |
| Ejector rod positions | Position drawing required | |
| Ejector coupling | Thread or coupling standard | |
| Ejector return method | Machine return, spring return or mold return pin | |
| Ejection sequence | Single or multiple-stage ejection | |
| Robot signal requirement | Confirmation signal after ejection |
SECTION E — INJECTION UNIT INFORMATION
| Item | Information Required | Buyer Input |
| Screw diameter | Actual screw size installed | |
| Maximum shot volume | cm³ | |
| Maximum shot weight | State the reference resin | |
| Maximum injection pressure | Available injection pressure | |
| Plasticizing capacity | kg/h or g/s | |
| Maximum injection rate | cm³/s or g/s | |
| Nozzle tip radius | Machine nozzle radius | |
| Nozzle hole diameter | Machine nozzle outlet diameter | |
| Nozzle projection | Distance from platen surface | |
| Locating ring diameter | Machine platen locating hole | |
| Purging and material change | Required frequency | |
| Special resin requirements | PVC, glass fiber, high temperature or corrosive resin |
SECTION F — CORE PULL AND MOLD FUNCTIONS
| Item | Information Required | Buyer Input |
| Hydraulic core-pull circuits | Number available | |
| Core-pull pressure | Available hydraulic pressure | |
| Core-pull flow | Available flow rate | |
| Core-pull sequence | Before opening, during opening or after opening | |
| Pneumatic circuits | Number and pressure | |
| Unscrewing control | Hydraulic, servo or rack system | |
| Hot runner zones | Number of temperature-control zones | |
| Valve gate control | Pneumatic, hydraulic or electric | |
| Mold sensors | Position, pressure or cavity sensors | |
| Electrical voltage | Local power supply | |
| Plug and connector standard | Customer or machine standard |
SECTION G — COOLING AND UTILITY INFORMATION
| Item | Information Required | Buyer Input |
| Cooling water temperature | Required mold inlet temperature | |
| Water pressure | Available plant pressure | |
| Water flow | Available flow per circuit | |
| Water quality | Treated, softened or tower water | |
| Mold temperature controller | Required or not required | |
| Chiller capacity | Available or planned | |
| Cooling connector type | Thread and quick-coupling standard | |
| Water manifold location | Operator side or non-operator side | |
| Compressed air | Pressure and connection size | |
| Hydraulic oil connection | Hose and fitting standard | |
| Electrical supply | Voltage, frequency and phases | |
| Grounding requirement | Local electrical standard |
SECTION H — AUTOMATION AND PART REMOVAL
| Item | Information Required | Buyer Input |
| Part removal method | Manual, free drop or robot | |
| Robot type | Top-entry, side-entry or six-axis | |
| Robot payload | Part plus gripper weight | |
| Gripper dimensions | Required clearance inside mold | |
| Robot entry direction | Top, side or rear | |
| Part release position | Required mold opening distance | |
| Sprue removal | Robot, sprue picker or automatic separation | |
| Conveyor required | Yes or no | |
| Insert loading | Manual or automated | |
| Vision inspection | Required or not required | |
| Machine signal interface | EUROMAP or other interface | |
| Safety guarding | Cell layout and access requirements |
SECTION I — FACTORY AND INSTALLATION INFORMATION
| Item | Information Required | Buyer Input |
| Factory ceiling height | Required for crane and robot | |
| Crane capacity | Maximum lifting capacity | |
| Factory door dimensions | Machine and mold access | |
| Floor loading capacity | Machine and mold weight | |
| Machine layout | Distance between production cells | |
| Main electrical supply | Voltage, frequency and power capacity | |
| Cooling system | Central or individual | |
| Air compressor capacity | Available compressed air | |
| Material storage | Bags, silos or central feeding | |
| Resin drying | Dryer or dehumidifying system | |
| Scrap handling | Crusher, recycling or external disposal | |
| Maintenance area | Mold repair and machine maintenance space | |
| Spare-part storage | Recommended critical spare parts | |
| Local technical support | Machine, mold and auxiliary equipment service |
Why Tie-Bar Space Is Not the Same as Platen Size
Buyers sometimes check the platen dimensions but forget the tie-bar spacing.
These are different measurements.
The platen dimensions determine the available mounting surface.
Tie-bar spacing determines whether the mold can physically enter the clamping unit.
A mold may fit on the platen but still be too wide to pass between the tie bars.
The following dimensions should therefore be checked separately:
- Mold width and height
- Horizontal and vertical tie-bar spacing
- Platen width and height
- Clamping-slot position
- Safety-door opening
- External cylinder and manifold dimensions
External components should be included in the final mold envelope drawing.
Why Mold Thickness Must Be Confirmed
Every injection molding machine has a permitted mold thickness range.
If the mold is thinner than the machine’s minimum mold height, the machine may not be able to build correct clamping force without additional spacer plates.
If the mold is thicker than the maximum permitted mold height, the mold cannot be installed.
The mold supplier should confirm:
- Final mold thickness
- Minimum machine mold height
- Maximum machine mold height
- Space required for insulation plates
- Space required for hot runner connectors
- Space required for hydraulic systems
Do not rely only on the preliminary mold estimate.
The final mold thickness should be checked again after the 3D mold design is completed.
How to Check the Required Opening Stroke
The required opening stroke should be calculated according to the actual part-removal method.
For a simple shallow product, the required opening may include:
- Product depth
- Ejection stroke
- Safety allowance
For a deep product or robot-removal application, it may include:
- Product depth
- Core depth
- Ejection distance
- Robot gripper thickness
- Robot movement clearance
- Sprue length
- Safety allowance
For example, a deep plastic crate may require more opening space than its product height because the crate must clear the core before it can move sideways or be gripped by a robot.
The mold supplier, machine supplier and automation supplier should approve the same part-removal drawing.
How to Check Injection Capacity
Shot weight should not be compared only with the advertised maximum machine shot weight.
The total shot includes:
- Finished plastic parts
- Cold runner
- Sprue
- Overflow or cold-slug wells
- Process allowance
The required shot volume must also be converted according to the density of the actual plastic.
A machine specification may state shot weight using polystyrene as the reference material.
The real shot weight for PP, HDPE, PA or filled compounds will be different.
As a general project principle, the required shot should remain within a practical operating range of the injection unit rather than operating continuously at the absolute minimum or maximum capacity.
The supplier should check:
- Total shot volume
- Actual resin density
- Screw diameter
- Injection pressure
- Injection rate
- Plasticizing capacity
- Residence time
- Expected cycle time
Why Clamping Force Is Not Selected by Part Weight
Clamping force is mainly related to projected area and cavity pressure, not part weight.
A large, thin automotive panel may weigh less than a thick technical component but require a larger clamping unit because of its projected area.
The preliminary clamping-force review should consider:
- Total projected area
- Number of cavities
- Runner projected area
- Resin flow characteristics
- Wall thickness
- Gate design
- Expected cavity pressure
- Safety margin
For a new factory, machine selection should begin with the largest projected area and most demanding mold planned for each machine group.
Locating Ring and Nozzle Compatibility
The locating ring aligns the mold sprue bushing with the machine injection nozzle.
The buyer should confirm:
- Machine locating-hole diameter
- Mold locating-ring diameter
- Nozzle tip radius
- Sprue-bushing radius
- Nozzle-hole diameter
- Sprue-bushing inlet diameter
- Nozzle projection
- Required nozzle contact force
If the radii or diameters do not match correctly, the system may experience:
- Material leakage
- Sprue sticking
- Misalignment
- Damage to the sprue bushing
- Unstable injection
- Material accumulation around the nozzle
These dimensions should be shown on the machine platen drawing and mold assembly drawing.
Core Pull, Unscrewing and Special Mold Functions
A mold with side cores, hydraulic cylinders or unscrewing mechanisms requires more than a standard open-and-close machine cycle.
Before purchasing the machine, confirm:
- Number of hydraulic core-pull circuits
- Maximum oil pressure
- Available flow
- Sequence control
- Core position sensors
- Hydraulic connector standard
- Pneumatic valve-gate control
- Unscrewing motor control
- Mold protection logic
- Interface with robot and safety system
If a mold requires four independent hydraulic sequences but the machine provides only two core-pull circuits, additional control equipment may be necessary.
This should be identified before the machine order is finalized.
Cooling Capacity Must Match the Production Target
A new factory may purchase suitable machines and molds but underestimate the cooling system.
This can cause:
- Longer cycle time
- Unstable mold temperature
- Part deformation
- Inconsistent shrinkage
- Surface defects
- Excessive equipment downtime
Cooling-system planning should consider:
- Number of machines
- Resin type
- Part weight
- Cycle time
- Mold temperature
- Hydraulic oil cooling
- Ambient factory temperature
- Local water quality
- Future factory expansion
The cooling supplier should calculate the complete heat load rather than selecting a chiller only by machine tonnage.
Mold Handling and Factory Access
Large injection molds may weigh several tons.
The factory should be able to receive, unload, store, move, install and maintain each mold safely.
Confirm:
- Container unloading method
- Factory entrance width and height
- Crane capacity
- Crane hook height
- Forklift capacity
- Mold cart capacity
- Space between machines
- Mold-loading direction
- Maintenance-area capacity
- Mold storage racks
A machine may have enough tie-bar spacing, but the factory crane or machine-side access may still prevent safe mold installation.
A Recommended Purchasing Sequence for a New Factory
Step 1: Define the Products
Collect the part drawings, materials, annual quantities, quality requirements and packaging requirements.
Step 2: Complete a Preliminary DFM Review
Review wall thickness, draft angle, ribs, undercuts, gate options and expected molding risks.
Step 3: Prepare Preliminary Mold Concepts
Estimate cavity number, mold dimensions, mold weight, runner type and special functions.
Step 4: Select the Machine Range
Check projected area, shot size, tie-bar spacing, mold thickness, opening stroke, ejector system and core-pull requirements.
Step 5: Freeze the Machine Specification
Obtain the official machine specification sheet and platen drawing.
Step 6: Finalize the Mold Design
Design the mold according to the confirmed machine dimensions and interfaces.
Step 7: Review Automation and Utilities
Confirm robot access, cooling, air, power, material feeding and safety signals.
Step 8: Conduct a Compatibility Review
The machine supplier, mold supplier and automation supplier should review one shared compatibility document.
Step 9: Approve the Final Layout
Check machine spacing, crane access, material flow, operator safety and future expansion.
Step 10: Plan Trials and Acceptance
Define where the mold will be tested, which machine will be used and what acceptance criteria must be met.
Minimum Information to Send a Mold Supplier
When requesting a mold quotation, send at least:
- 2D and 3D part drawings
- Plastic material
- Part weight
- Annual production quantity
- Required cavity number
- Surface requirement
- Target cycle time
- Mold life target
- Injection molding machine brand
- Complete machine model
- Tie-bar spacing
- Minimum and maximum mold thickness
- Opening stroke
- Maximum daylight
- Ejector stroke and arrangement
- Locating-ring diameter
- Nozzle radius
- Core-pull circuits
- Destination country
- Customer mold standard
If the machine has not yet been purchased, tell the mold supplier clearly.
The mold supplier can then provide preliminary mold dimensions and machine requirements before the machine order is finalized.
Minimum Information to Send a Machine Supplier
When requesting an injection molding machine quotation, send:
- Product drawing
- Plastic material
- Part weight
- Runner weight
- Number of cavities
- Mold dimensions
- Mold thickness
- Mold weight
- Projected area
- Required opening distance
- Ejector requirements
- Core-pull requirements
- Target cycle time
- Annual production quantity
- Robot requirements
- Local voltage and frequency
Do not select the machine only by clamping-force tonnage.
Common Purchasing Mistakes
Mistake 1: Buying the Machine Before Estimating the Mold
The machine may later prove too small in tie-bar spacing, shot capacity or opening stroke.
Mistake 2: Selecting the Machine Only by Part Weight
Part weight does not determine clamping force or mold dimensions.
Mistake 3: Ignoring the Runner Weight
Cold runners can significantly increase the required shot size.
Mistake 4: Using the Maximum Advertised Shot Weight
The advertised value may be based on PS rather than the actual resin.
Mistake 5: Checking Opening Stroke but Not Maximum Daylight
The mold may fit, but the remaining opening space may be insufficient.
Mistake 6: Forgetting Ejector-Rod Positions
The machine ejector may not connect correctly to the mold.
Mistake 7: Ignoring External Mold Components
Hydraulic cylinders and manifolds may interfere with tie bars or safety doors.
Mistake 8: Purchasing the Robot Too Late
The mold opening, part orientation and gripper clearance may not support the selected robot.
Mistake 9: Underestimating Cooling Capacity
The factory cannot achieve the target cycle time even though the mold and machine are suitable.
Mistake 10: Using Different Technical Data Between Suppliers
The mold supplier, machine supplier and robot supplier must work from the same approved specification.
Frequently Asked Questions
What machine information does an injection mold supplier need?
The mold supplier should receive the complete machine model and technical data, including tie-bar spacing, platen dimensions, mold thickness range, opening stroke, maximum daylight, ejector arrangement, locating ring, nozzle radius, shot capacity and core-pull connections.
Can a mold fit the platen but not fit between the tie bars?
Yes. The platen mounting surface may be large enough, while the clear distance between the tie bars is too small for mold installation.
Is maximum opening stroke the same as maximum daylight?
No. Opening stroke is the movement of the moving platen. Maximum daylight is the total distance between the platens when fully open and usually includes the installed mold-height allowance.
How much opening stroke does a mold need?
It depends on product depth, core depth, ejection stroke, sprue length, robot clearance and removal direction. The correct value should be calculated from the part-removal drawing.
Why is the ejector layout important?
The machine ejector rods must apply force at the correct positions on the mold ejector system. Incorrect positioning can cause uneven ejection, plate deformation or failure to eject the part.
Can one injection molding machine run many different molds?
Yes, provided each mold falls within the machine’s clamping force, shot capacity, tie-bar spacing, mold thickness, opening, ejector and interface limits.
Should the mold or machine be purchased first?
Neither should be finalized independently. The product and preliminary mold concept should first define the machine requirements, after which the final mold should be designed around the confirmed machine specification.
What is the most important document for mold and machine matching?
The most useful document is a complete machine platen and mold-installation drawing showing tie bars, platens, locating ring, nozzle, ejector positions, mounting holes and installation limits.
Does a larger machine always solve compatibility problems?
No. A larger machine may increase investment, power use, floor space and operating cost. The goal is to select the smallest practical machine that safely meets the complete process requirements.
Who should approve the compatibility checklist?
Ideally, it should be reviewed by the buyer, mold supplier, injection molding machine supplier and automation supplier before final orders are placed.
Final Checklist Before Placing an Order
Before approving the machine and mold purchase, confirm that:
- The mold passes between the tie bars
- The mold fits the platen
- The mold thickness is within the machine range
- The remaining opening is sufficient for part removal
- Maximum daylight is sufficient
- The ejector stroke and positions match
- The locating ring fits
- The nozzle and sprue bushing match
- The shot size is suitable for the actual resin
- The injection pressure and rate are sufficient
- The clamping force is based on projected area
- Hydraulic core-pull circuits are sufficient
- Hot runner zones can be controlled
- Cooling capacity supports the target cycle
- The robot has enough clearance
- The mold weight is within the machine and crane limits
- Utility connections match local standards
- All suppliers are using the same approved data
Conclusion
A successful injection molding factory does not begin by purchasing machines, molds and auxiliary equipment separately.
It begins by defining the plastic products and designing a complete production system around them.
Tie-bar spacing, opening stroke and ejection are three critical parameters, but they are only part of the compatibility review.
The machine, mold, injection unit, cooling system, robot, utilities and factory layout must work together.
Completing the compatibility checklist before placing orders can prevent expensive modifications, delayed production and oversized equipment.
For a new injection molding factory, this coordination is one of the most important steps in the entire investment project.
Call to Action
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