Before design review
- Send bag drawings and samples
- Identify fin or lap seal
- Provide film structure and reel data
- Show the dosing outlet and product size
VFFS forming system
How does a VFFS forming shoulder work?
A VFFS forming shoulder changes a flat film web into a tube around the product path. Its geometry must suit the bag, film and seal arrangement, because the forming set controls how evenly the web bends, where its edges meet and how the finished bag leaves the machine.
Direct answer
The forming shoulder is a shaped film path, not a generic funnel.
The VFFS forming shoulder guides the moving film through a controlled three-dimensional curve and wraps it around a forming tube. The tube provides the product passage and helps define the bag cross-section. Film then meets at the vertical seal before the horizontal jaws create the bag ends. A suitable forming set allows the web to move without excessive drag, wrinkles or sideways force.
Follow the film path from reel to tube
Film approaches the shoulder as a flat web under controlled tension. The shoulder turns and folds the web while keeping both edges on a predictable path. Pull belts or another film-drive arrangement then draw the formed tube downward. The vertical sealing unit joins the edges as a fin or lap seal, depending on the film and pack design.
The shoulder cannot correct an unstable reel, badly aligned guides or unsuitable film by itself. Those inputs must arrive consistently so the shaped surface can do the same work on every cycle.
Match geometry to the finished bag
Bag width is only one input. Seal width, fin or lap orientation, gussets, product clearance, film stiffness and required bag shape affect the forming geometry. A bag that is nominally the same width may need a different forming set when the film structure or seal arrangement changes.
The product path also matters. Large pieces, fragile product or a wide dosing outlet may need more clearance through the tube than a fine powder dose, even where the finished bag dimensions are similar.
Separate forming faults from web-control faults
Wrinkles, an off-centre back seal or film wandering can originate before the shoulder, at the forming set or after the film has formed. Record where the first visible deviation occurs. Check reel alignment, guide rollers, tension, pull belts, forming-set seating, cleanliness and vertical-seal position before changing several variables at once.
A stable mark reading does not prove stable film movement. Printed-film registration can be correct at the sensor while the web shifts mechanically on its way through the forming path.
Define change parts and setup evidence
A new forming shoulder or tube should have a clear format identity and installation method. Record the matching film width, bag drawing, seal arrangement, product-clearance requirement and recipe. If the machine runs several formats, identify which guides, belts, jaws or product-contact parts change with the forming set.
During a trial, retain packs from start-up and stable running. Check back-seal position, wrinkles, bag symmetry, cut position and whether the product falls cleanly through the tube.
Decision aid
Inputs that control forming-set selection
Use the table as a design brief. Exact geometry must be confirmed for the real machine, film and pack.
| Input | Why it matters | Evidence to provide |
|---|---|---|
| Finished bag geometry | Controls cross-section, edge meeting position and any gusset or shape feature. | Dimensioned bag drawing and approved sample where available. |
| Film construction | Changes stiffness, friction, curl, seal method and how the web bends. | Full structure, width, thickness, unwind and production-intent trial reel. |
| Vertical seal | Fin and lap seals bring the film edges together differently. | Required seal style, width, orientation and sealant-layer information. |
| Product path | Sets tube clearance and the risk of product contact, bridging or damage. | Maximum piece size, dosing outlet, fill volume and product behaviour. |
| Format range | Shows whether one set is enough or several change parts are needed. | All SKU drawings, film specifications and expected change sequence. |
Quotation preparation
Information to prepare before the machinery review
During the trial
- Check back-seal position
- Inspect wrinkles and web marks
- Observe product clearance
- Record setup and first accepted pack
For repeat changeover
- Label each change part
- Store the approved recipe
- Define cleaning and inspection
- Confirm the restart sample check
Buyer questions
Questions buyers ask about VFFS forming shoulders
What does a VFFS forming shoulder do to the film web?
A VFFS forming shoulder bends and wraps a flat film web around a forming tube so its edges meet consistently for the vertical seal. The shaped path must distribute the change of direction without creating excessive drag or wrinkles, while the tube leaves a clear route for the product dose.
Why can the same bag width require a different forming set?
The same nominal width can use a different film structure, seal style, gusset, product clearance or bag cross-section. Those factors change how the web must bend and where its edges meet. Bag width should therefore be considered with the full pack drawing and film specification, not as a standalone forming-set size.
What signs suggest the forming set does not match the film or bag?
Persistent wrinkles, edge misalignment, back-seal movement, excessive drag, uneven bag shape or repeatable film damage near the shoulder can indicate a mismatch. Similar symptoms can also come from reel alignment or tension, so the fault should be traced from the incoming web through the forming set before the part is rejected.
Can one forming shoulder make every bag size?
No. Bag length can often change through the recipe, but bag width and cross-section are governed by the forming geometry. Some nearby formats may share a set, while wider, narrower, gusseted or differently sealed bags need another shoulder or tube. The usable family must be confirmed from all SKU drawings and films.
Should the forming shoulder be trialled with printed film?
Use production-intent printed film where registration, artwork position or surface behaviour matters. Plain film can help establish basic forming and sealing, but it does not prove mark sensing, print repeat, code position or the running behaviour of the approved printed reel.
Application review