File is not getting saved using paperclip

Hi all I have a form which contains attachments but the attachment is
not getting created in file system and the fields for the attachment
in DB is not getting filled when a new form is created .

I'm using paperclip

I hope the problem is with view part html=>:multipart (as I'm using a
single form to create multiple instances)

My Controller:

def create
  @ins=params[:ins].values.collect{|ins|InsPol.new(ins)}
    respond_to do |format|
    if @ins.all?(&:valid?)
      @ins.each(&:save!)

     format.html { redirect_to :action => 'index'}
    else

        format.html {render :action => 'new'}

     end
end

def new
     @ins = Array.new(3.times){InsPol.new}
end

  My view:

<%= form_tag({:action => :create}, {:multipart => true}) %>
   <% @ins.each_with_index do |ins, index| %>
    <% fields_for "ins[#{index}]", ins do |f| %>
        <%= f.text_field :pol_number%>
       <%= f.file_field :attachment%>
    <% end %>
     <br/>
     <% end %>
        <%= submit_tag "Save"%>
</form>

My Model:

class InsPol < ActiveRecord::Base
has_attached_file :attachment

end

Moreover i have All the db migration for this attachment using
paperclip and paperclip installed properly

Plz help me in this regard